Exchange Of Genetic Information Research Articles

Telomeres of the linear chromosomes of Lyme disease spirochaetes: nucleotide sequence and possible exchange with linear plasmid telomeres

Bacteria of the spirochaete genus Borrelia have linear chromosomes about 950 kbp in size. We report here that these linear chromosomes have covalently closed hairpin structures at their termini that are similar but not identical to those reported for linear plasmids carried by these organisms. Nucleotide sequence analysis of the chromosomal telomeric regions indicates that unique, apparently functional genes lie within a few hundred bp of each of the telomeres, and that there is an imperfect 26 bp inverted repeat at the two telomeres. In addition, we characterize a major chromosomal length polymorphism within the right telomeric regions of various Borrelia isolates, and show that sequences similar to those near the right telomere are often found on linear plasmids in B. burgdorferi (sensu stricto) isolates from nature. Sequences similar to a number of other regions of the chromosome, including those near the left telomere, were not found on B. burgdorferi plasmids. These observations suggest that there has been historical exchange of genetic information between the linear plasmids and the right end of the linear chromosome.

Experimental surgery to create subgenomes of Bacillus subtilis 168.

The 4,188-kb circular genome of Bacillus subtilis 168 was artificially dissected into two stable circular chromosomes in vivo, one being the 3,878-kb main genome and the other the 310-kb subgenome that was recovered as covalently closed circular DNA in CsCl-ethidium bromide ultracentrifugation. The minimal requirements to physically separate the 310-kb DNA segment out of the genome were two interrepeat homologous sequences and an origin of DNA replication between them. The subgenome originated from the 1,255-1, 551-kb region of the B. subtilis genome was essential for the cell to survive because the subgenome was not lost from the cell. The finding that the B. subtilis genome has a potential to be divided and the resulting two replicons stably maintained may shed light on origins and formation mechanisms of giant plasmids or second chromosomes present in many bacteria. Similar excision or its reversal process, i.e., integration of large sized covalently closed circular DNA pieces into the main genome, implies significant roles of subgenomes in the exchange of genetic information and size variation of bacterial genomes in bacterial evolution.

Double-Strand Break-Induced Recombination in Eukaryotes

Genetic recombination is of fundamental importance for a wide variety of biological processes in eukaryotic cells. One of the major questions in recombination relates to the mechanism by which the exchange of genetic information is initiated. In recent years, DNA double strand breaks (DSBs) have emerged as an important lesion that can initiate and stimulate meiotic and mitotic homologous recombination. In this review, we examine the models by which DSBs induce recombination, describe the types of recombination events that DSBs stimulate, and compare the genetic control of DSB-induced mitotic recombination in budding and fission yeasts.

Doing the Conjugative Two-step: Evidence of Recipient Autonomy in Retrotransfer

Bidirectional exchange of genetic information, called retrotransfer, during bouts of bacterial conjugation has drawn the interest of those concerned with the risk of releasing genetically engineered microbes, the fluidity of genes among species, and the mechanism of DNA transport between cells. The phenomenon has generated two models in explanation, both of which yield highly testable predictions. The first model, called the one-step, predicts that the flow of genes from recipient bacteria to donor bacteria is mechanistically distinct from, but dependent on, conjugation between donors and recipients. The second model, called the two-step, predicts that the same genetic requirements and mechanistic constraints apply to the process of gene flow from recipients to donors as for gene flow from donors to recipients. The requirement for expression of at least 10 plasmid-encoded genes in recipients, sensitivity of the reverse flow (recipient to donor) to restriction of DNA transferring from the donor, and the requirement of an additional 30-90 min for DNA to flow from recipients back to donors are predictions of the two-step model and directly refute the one-step model. Retrotransfer of genes to donors during conjugation remains genetically and physically indistinguishable from two successive rounds of conjugation between neighbors.

Interchromosomal exchange of genetic information between gene arrangements on the third chromosome of Drosophila pseudoobscura.

During the last 60 years, the inversion polymorphism on the third chromosome of Drosophila pseudoobscura has become a case study of the evolution of linked blocks of genes, isolated from each other by the suppression of recombination in heterozygotes for different inversions. Due to its location within inverted regions in most gene arrangements, the amylase (Amy) gene region can be used to elucidate the molecular pattern of evolution in these inversions. We studied this region in the Tree Line phylad of gene arrangements, with regard to both restriction site polymorphisms (RSP) and nucleotide sequences. The analysis of restriction maps, encompassing 26 kb, corroborates the cytogenetic phylogeny established on the basis of inversion breakpoints. However, we found that the 2.7 kb of nucleotide sequences of the AmyI gene are identical in both Estes Park and Hidalgo arrangements, despite the fact that these inversions arose independently from Tree Line. These contrasting results suggest that a homogenizing force, most likely gene conversion, is able to bring about localized exchanges between otherwise isolated gene arrangements.

White-Tailed Deer Restoration to the Southeastern United States: Evaluating Genetic Variation

Protective legislation and restocking were used to restore white-tailed deer (Odocoileus virginianus) to the southeastern United States (U.S.) following declines that occurred during the nineteenth century. Although stocking and protection of native herds are often key components of deer management programs, the degree to which these strategies contributed to recovery of southeastern white-tailed deer has not been determined. We used mitochondrial DNA (mtDNA) restriction-site variation and allozyme diversity to characterize gene flow patterns and genetic differentiation among white-tailed deer populations in the southeastern U.S. and evaluated the effectiveness of management programs for restoring white-tailed deer to the region. Compared with white-tailed deer in northern areas of North America, deer in the southeastern U.S. exhibited a high level of mtDNA subdivision (Gs, = 0.621) that may be attributable to site philopatry of females. Relative to mtDNA, the extent of allozyme differentiation (FsT = 0.153) indicated a bias in dispersal (gene flow) toward males (3:1), suggesting that managers should regulate the degree to which males are preferentially harvested to preserve the exchange of genetic information among populations. Geographic patterns of genetic variation in white-tailed deer were congruent with those in unrelated taxa, implicating the common influence of historical biogeographic events in shaping contemporary genetic structure. Similarities in geographic variation between white-tailed deer and other vertebrates inhabiting this region indicated that deer populations in the southeastern U.S. are descended from native herds and that relocated deer have contributed insignificantly to the genetic composition of extant populations. J. WILDL. MANAGE. 58(4):686-697

Genes for mast-cell serine protease and their molecular evolution.

Trypsin-related serine proteases are encoded by a very large gene family in mammals. We describe here a comparative analysis of the genomic DNA sequences of mouse, rat, and human mast-cell-specific serine protease genes. Strong evidence was found for multiple exchanges of genetic information between closely related members of this gene family. The 5' regulatory regions of MMCP-1 and MMCP-L share a remarkably high degree of sequence identity (98%), starting 10 base pairs downstream of exon 1 and extending to the end of the presently sequenced region at position -1347 of the MMCP-1 gene. The remaining parts of the two genes share approximately 80% sequence identity. Evidence for at least two additional, but not so recent, exchanges was found in the 3' regions of the MMCP-4 and MMCP-L genes and in the 5' regions of the genes for MMCP-1 and MMCP-2. The 5' regulatory regions of all presently characterized mouse mast-cell-specific chymotrypsin-like serine protease genes exhibit over 88% sequence identity in the region from the transcription initiation site to approximately position -600. An exception is MMCP-5 which is the most distantly related member of this subfamily. The high degree of sequence similarities indicates a strong evolutionary homogenization of the 5' regulatory region, possibly by several gene conversion events. In addition, several insertions of genetic information have been identified in genes for mast-cell chymases and genes for T-cell granzymes. A number of these have been found to represent repetitive sequences, such as L1. The previously characterized tissue-specific enhancer element of the RMCP II gene was identified as a member of a middle repetitive sequence. A cDNA for a newly discovered pseudogene, closely related to the mouse mast cell chymases was isolated by polymerase chain reaction amplification from a mouse connective tissue-like mast cell line. The structure of this cDNA is presented. We also present the characterization of a novel spliced variant of MMCP-6 that contains an alternative 3' terminal exon (exon 6). The function of this variant, if any, is still unknown. A comparative analysis of amino acid sequence identities between different hematopoietic serine proteases shows that a high degree of sequence similarity does not always correlate with relateness in cleavage specificity. This indicates that the substrate specificity evolved with a higher evolutionary rate than the degree of overall amino acid sequence identity of these proteases.

Presence of the Listeria tetracycline resistance gene tet(S) in Enterococcus faecalis

Two hundred thirty-eight tetracycline- and minocycline-resistant clinical isolates of Enterococcus and Streptococcus spp. were investigated by dot blot hybridization for the presence of nucleotide sequences related to tet(S) (first detected in Listeria monocytogenes BM4210), tet(K), tet(L), tet(M), tet(O), tet(P), and tet(Q) genes. The tet(S) determinant was found in 22 strains of Enterococcus faecalis, associated with tet(M) in 9 of these isolates and further associated with tet(L) in 3 of these strains. tet(M) was detected in all strains of Streptococcus spp. and in all but 10 isolates of Enterococcus spp.; tet(L) was found in 93 enterococci and tet(O) was found in single isolates of E. faecalis and Streptococcus milleri. No hybridization with the tet(K), tet(P), and tet(Q) probes was observed. Transfer of tet(S) by conjugation to E. faecalis or to E. faecalis and L. monocytogenes was obtained from 8 of the 10 E. faecalis strains harboring only this tet gene. Hybridization experiments with DNAs of four donors and of the corresponding transconjugants suggested that tet(S) was located in the chromosome. These results indicate that the genetic support of tet(S) in E. faecalis is different from that in L. monocytogenes, where it is carried by self-transferable plasmids, and confirm the notion of exchange of genetic information between Enterococcus and Listeria spp. in nature.

Tansley Review No. 70 Signal transduction during fertilization in algae and vascular plants

summaryFertilization involves interaction between two gametes and exchange of genetic information. In addition, information is transferred which results in triggering of the particular cellular and developmental responses of the organism. This review considers the cellular signals involved during different stages of gamete interactions in plants, including gamete attraction, recognition, fusion, zygotic activation and development. A wide range of signalling mechanisms can be seen to operate during fertilization, reflecting both the diversity of systems bringing gametes together and the different cellular responses to fertilization throughout the plant kingdom. Moreover, signals involved in triggering early development following gamete fusion appear to differ significantly even between species showing at least superficially similar cellular responses. Much of our current understanding comes from studies of a few easily accessible systems though recent developments in gamete isolation, in vitro fertilization and embryo culture should increase the scope for studies of signalling mechanisms in vascular plants. Contents Summary 399 I. Introduction 400 II. Chlamydomonas: interaction between structurally identical gametes 401 III. Fucoid algae: a simple oogamous system 409 IV. Vascular plants 412 V. Concluding remarks 418 Acknowledgements 418

The Ribosomal RNA Gene Region in Acanthamoeba castellanii Mitochondrial DNA: A Case of Evolutionary Transfer of Introns between Mitochondria and Plastids?

Acanthamoeba castellanii, an amoeboid protozoan, occupies an intriguing position in phylogenetic trees based on nuclear rRNA sequences, branching together with or near (as an outgroup to) green algae and land plants. To gain insight into the organization, expression and evolutionary affiliations of the mtDNA of this non-photosynthetic protist, we determined the sequence of a 7778 base-pair region containing the single-copy large subunit (LSU) and small subunit (SSU) rRNA genes (rnl and rns, respectively) of the ∼40 kilobase-pair A. castellanii mitochondrial genome. We also sequenced the 5′- and 3′-terminal portions of the corresponding LSU and SSU rRNAs. In A. castellanii mtDNA, rnl is flanked both upstream and downstream by a cluster of five tRNA genes, with rns and then cox1 (the cytochrome oxidase subunit 1 gene) following immediately further downstream. These genes are all in the same transcriptional orientation and are separated by only short non-coding spacers. Although rnl and rns are organized in a novel way in A. castellanii mtDNA, their SSU and LSU rRNA products are strikingly similar to their eubacterial homologs in primary sequence, secondary structure and post-transcriptional modification. In these characteristics, the A. castellanii mitochondrial rRNAs much more closely resemble their counterparts in land plants than do the corresponding mitochondrial rRNAs in the green alga, Chlamydomonas reinhardtii. Although no intervening sequences have so far been found in the mitochondrial rnl of angiosperms (flowering plants), A. castellanii mitochondrial rnl contains three group I introns, all located within highly conserved regions in the 3′-half of the gene and each possessing a free-standing open reading frame (ORF). The insertion site of one of these introns is identical to that of the single group I intron in the chloroplast rnl of C. reinhardtii, and sequence comparison reveals that these two introns (one mitochondrial, the other chloroplast) are structurally homologous both within the core region and within the ORFs they encode. These observations are indicative of intron movement between mitochondria and chloroplasts, either intra cellularly in a photosynthetic, remote common ancestor of A. castellanii and C. reinhardtii or, more recently, as a result of an inter cellular exchange of genetic information.

Genetics of ectomycorrhizal fungi: progress and prospects

The variability within and among ectomycorrhizal species provides a substantial genetic resource and the potential to increase forest productivity and environmental sustainability. Two parallel and interacting approaches, classical and molecular genetics, are being developed to acquire the genetic information underpinning selection of improved ectomycorrhizal strains. Determining the genetic traits of the fungi which contribute to symbiosis and plant function are being followed using natural variability combined with classical and molecular genetic manipulations. Classical and molecular manipulations for breeding rely on key information including sexual and parasexual reproduction, postmeiotic nuclear behaviour, mating-types and vegetative incompatibility mechanisms. Progress in the manipulation of genomes of ectomycorrhizal fungi will depend on efficient methods for gene cloning and DNA transformation. Gene transfer into fungal cells have been shown to be successful and include treatment of protoplasts and intact mycelium with naked DNA in the presence of polyvalent cations, electroporation, and microbombardment. The merits and limitations of these methods are discussed. Using this technology the expression of foreign DNA, the functional analysis of fungal DNA sequences, as well as molecular exploitation for commercial purposes can be carried out. This review concentrates on these aspects of fungal molecular biology and discusses the applications of the experimental systems that are currently available to ectomycorrhizal fungi. As it is essential to be able to define the traits which a breeder is seeking to improve, availability of genetically defined strains that are isogenic for a character or differ only in one character and a thorough knowledge of the biochemistry of the symbiosis will be necessary before any genetic manipulation be carried out. Genetic variability of ectomycorrhizal strains has been assessed by DNA fingerprinting. This approach allows the evaluation of DNA variability and the exchange of genetic information in natural populations, the identification of species and isolates by DNA polymorphisms, and tracking the environmental fate of the introduced fungi to determine their survival, growth, and dissemination within the soil.

Monitoring of resistant organisms in man and identification of their origin

Information on the epidemiology of bacterial resistance is fragmentary despite an enormous number of publications since the introduction of antibiotics to human medicine, and remains a field of speculation mixed and influenced by fear of the total collapse of antimicrobial chemotherapy by development of resistance (for review see Wiedermann et al., 1986). Bacteria have evolved mechanisms to withstand the attack of antibiotics and, in parallel, mechanisms for the spread of these characters to other bacteria by means of exchange of genetic information. However the development of resistance cannot be generalized. Staphylococcus aureus gained penicillin resistance within a few years after the introduction of this drug, while Streptococcus pyogenes remains 100% susceptible to penicillin, despite of the long use of penicillins in huge quantities. Thus any statement about the development and epidemiology of resistance has to be addressed specifically to a drug, a bacterial species, and a location. Until now there is no identifiable general trend, which would allow us to deduce a general picture or a future development from a limited database. In this paper long term multicentre studies are presented to demonstrate the area of concern for the treatment of human infections. In this context it is of specific interest to try and trace the origin of bacteria which cause infections in humans.

Risks connected with the use of conventional and genetically engineered vaccines.

A review is given of real and potential risks connected with the use of conventional and genetically engineered live and dead vaccines. Special attention is given to live carrier vaccines expressing one or more heterologous genes of other microorganisms. Because most carrier vaccines are still in an experimental phase, there is only limited experience with the risks of carrier vaccines. There are three potential risks of live carrier vaccines which will be discussed: 1. Changes in cell, tissue, of host tropism, and virulence of the carrier through the incorporation of foreign genes. 2. Exchange of genetic information with other vaccine or wild-type strains of the carrier organism. 3. Spread in the environment. Only limited experimental data are available on changes in biological behaviour of microorganisms through the incorporation of foreign genes. For example, there are indications that vaccinia virus carrying the attachment protein G of respiratory syncytial virus (RSV) replicates better in lungs of mice than vaccinia virus carrying other genes of RSV. Poxviruses carry genes that probably determine their replication in different hosts. Exchange of such host tropism genes might alter their host spectrum. Recombination between herpesvirus vaccine or wild-type strains may lead to the appearance of virulent strains with of without heterologous genes. Before carrier vaccines are applied, these risks must be thoroughly evaluated case-by-case. Potential methods for the design of safe carrier vaccines are discussed.

RNA recombination in animal and plant viruses.

An increasing number of animal and plant viruses have been shown to undergo RNA-RNA recombination, which is defined as the exchange of genetic information between nonsegmented RNAs. Only some of these viruses have been shown to undergo recombination in experimental infection of tissue culture, animals, and plants. However, a survey of viral RNA structure and sequences suggests that many RNA viruses were derived form homologous or nonhomologous recombination between viruses or between viruses and cellular genes during natural viral evolution. The high frequency and widespread nature of RNA recombination indicate that this phenomenon plays a more significant role in the biology of RNA viruses than was previously recognized. Three types of RNA recombination are defined: homologous recombination; aberrant homologous recombination, which results in sequence duplication, insertion, or deletion during recombination; and nonhomologous (illegitimate) recombination, which does not involve sequence homology. RNA recombination has been shown to occur by a copy choice mechanism in some viruses. A model for this recombination mechanism is presented.

RNA recombination in animal and plant viruses.

An increasing number of animal and plant viruses have been shown to undergo RNA-RNA recombination, which is defined as the exchange of genetic information between nonsegmented RNAs. Only some of these viruses have been shown to undergo recombination in experimental infection of tissue culture, animals, and plants. However, a survey of viral RNA structure and sequences suggests that many RNA viruses were derived form homologous or nonhomologous recombination between viruses or between viruses and cellular genes during natural viral evolution. The high frequency and widespread nature of RNA recombination indicate that this phenomenon plays a more significant role in the biology of RNA viruses than was previously recognized. Three types of RNA recombination are defined: homologous recombination; aberrant homologous recombination, which results in sequence duplication, insertion, or deletion during recombination; and nonhomologous (illegitimate) recombination, which does not involve sequence homology. RNA recombination has been shown to occur by a copy choice mechanism in some viruses. A model for this recombination mechanism is presented.

Genetic recombination in RNA viruses.

Recombination in RNA viruses involves the exchange of genetic information between two nonsegmented RNA genomes, as distinct from the reassortment of RNA seen in viruses containing segmented genomes. The mechanism of RNA recombination appears to be similar to the generation of defective interfering (DI) RNA, since they both involve polymerase jumping during RNA synthesis. However, unlike the production of DI RNA, which is a relatively common phenomenon among RNA viruses, RNA recombination has so far only been demonstrated in a few RNA viruses. Homologous RNA recombination, which is defined as the exchange of two comparable RNA regions at precise locations, was first detected in poliovirus by Hirst (1962) and Ledinko (1963) in the early 1960s. Soon after, another member of the pircornavirus family, foot-and-mouth disease virus (FMDV), an aphthovirus, also was shown to undergo recombination (Pringle 1965). Subsequently, a series of temperature-sensitive (ts) mutants was used to determine recombination frequencies and do obtain a linear genetic recombination map (Cooper 1968, 1977). The definitive evidence for the occurrence of RNA recombination eventually came from the biochemical analysis of protein and RNA structure of the recombinant viruses (King et al. 1982). The second virus family to be shown to undergo RNA recombination is coronavirus (Lai et al. 1985). And more recently, several plant viruses, including brome mosaic virus and cowpea chlorotic mottle virus, also have been shown to undergo RNA recombination in rare situations (Bujarski and Kaesberg 1986; Allison et al. 1990). Thus, RNA recombination is being recognized increasingly as a general biological phenomenon among RNA viruses and probably plays an important role in viral biology and virus evolution. This chapter will deal mainly with homologous RNA recombination and will not discuss DI RNA, which is one form of nonhomologous RNA recombination.

Allelic exchange in Escherichia coli using the Bacillus subtilis sacB gene and a temperature‐sensitive pSC101 replicon

To facilitate efficient allelic exchange of genetic information into a wild-type strain background, we improved upon and merged approaches using a temperature-sensitive plasmid and a counter-selectable marker in the chromosome. We first constructed intermediate strains of Escherichia coli K12 in which we replaced wild-type chromosomal sequences, at either the fimB-A or lacZ-A loci, with a newly constituted DNA cassette. The cassette consists of the sacB gene from Bacillus subtilis and the neomycin (kanamycin) resistance gene of Tn5, but, unlike another similar cassette, it lacks IS1 sequences. We found that sucrose sensitivity was highly dependent on incubation temperature and sodium chloride concentration. The DNA to be exchanged into the chromosome was first cloned into derivatives of plasmid pMAK705, a temperature-sensitive pSC101 replicon. The exchanges were carried out in two steps, first selecting for plasmid integration by standard techniques. In the second step, we grew the plasmid integrates under non-selective conditions at 42 degrees C, and then in the presence of sucrose at 30 degrees C, allowing positive selection for both plasmid excision and curing. Despite marked locus-specific strain differences in sucrose sensitivity and in the growth retardation due to the integrated plasmids, the protocol permitted highly efficient exchange of cloned DNA into either the fim or lac chromosomal loci. This procedure should allow the exchange of any DNA segment, in addition to the original or mutant allelic DNA, into any non-essential parts of the E. coli chromosome.

Modern pollen rain within and adjacent to two giant sequoia (Sequoiadendrongiganteum) groves, Yosemite and Sequoia national parks, California

Analysis of modern pollen (from polsters) and plant percentage coverage (from relevés) within and near two giant sequoia (Sequoiadendrongiganteum) groves provide data on the relationship between plant abundance and pollen dispersion. Most Sequoiadendron pollen is deposited within or near the groves, substantiating previously established theoretical models on pollen dispersion. Within the groves, Sequoiadendron is only slightly overrepresented by its pollen (R value average, 1.6). At the Tuolumne Grove, Sequoiadendron pollen averages 1.5% at stations within 450 m of the grove boundary. Pollen percentage is slightly higher (8%) for similar stations at Lost Grove. This contrasts with the more widely dispersed pollen of Pinus and Quercus, and the less widely dispersed Chrysolepis and Cornus. Patterns of pollen dispersal away from the groves are consistent with the prevailing wind direction and diurnal air mass movements. For Sequoiadendron, the relatively poor dispersal has implications for future paleoecologic studies interpreting the sedimentary pollen record from meadow sediment cores; and for understanding the exchange of genetic information between these trees that grow in stands somewhat isolated from each other.

Recombination between V H pseudogenes

The peculiar pattern of nucleotide differences between germline V H genes V104A/VAR104 and 122B could be the result of an exchange of genetic information through gene conversion. A palindromic sequence in one of the genes seems to have been the target site for the break that initiated recombination.

RISH VI: General evolutionary aspects of the immune system

Both the prokaryotic and eukaryotic cells are considered to have arisen from a common progenitor cell. The plasma membrane of the prokaryotic cell became specialized to carry out functions that the eukaryotic cell delegated to cellular organelles. Thus the plasma membrane of the eukaryotic cell remained flexible to evolutionary influences. Thus, provided the structural integrity of the plasma membrane was maintained, alterations within this infrastructure could be tolerated. This gave rise to basic speciation at the cellular level. Such differences in the plasma membrane of these primitive eukaryotic cells were of no importance until the dawn of sexual reproduction, then only like-cells could associate to exchange genetic information. Thus in the protozoa cell-surface, antigens are demonstrable in mating, whereas alloincompatability is intracellular. With the evolution of the Metazoa, in order for like-cells to identify each other, alloincompatability changed from intracellular expression to become expressed on the plasma membrane. Like-cell identification was derived and evolved from the basic feeding mechanism of primitive eukaryotic cells, which involved the induction of lectins that were expressed at the cell-surface. These lectins were induced by the RNA that was complementary to, and complexed with cell surface components of the organisms upon which the eukaryotic cells fed. This RNA was also inserted along with the lectin in the eukaryotic cell plasma membrane, and acted as a template for DNA synthesis. This DNA was then incorporated into the genome of the eukaryotic cell and it became an inheritable characteristic. Thus these lectins could be expressed intracellularly as well as on the plasma membrane. The intracellular expression of these inheritable lectins may have constituted intracellular-alloincompatability, as well as being used for feeding by agglutination of the organism on the plasma membrane of the eukaryotic cell. With the development of colony formation and the true metazoa, the cell-surface lectins became incorporated into cell-surface components for the identification of like-cells. This represents, in part, the histocompatability antigens of the organisms. At the same time, the lectins were also being increasingly used for the regulation of differentiation, and for what we would classify as immunological reactions. The lectins in the invertebrates are used in a similar manner to that of antibodies in the mammals. This commonality is based more on function than structure, and like the antibodies and HLA system, the lectins are derived from a common ancestral gene. The lectins in the invertebrates are thus inducible, specific for certain carbohydrates and are involved in humoral and cellular reactions.