Right Arm Of Linkage Group Research Articles

Genetics and some characteristics of acetate-requiring strains in Neurospora crassa.

Ten acetate-requiring mutants of Neurospora crassa were analyzed genetically and examined their growth and enzyme characteristics. It was found that four of the mutants occurred at the known two loci, ace-2 and suc, and the other six were identified as mutations at the new genes, ace-3, ace-4, ace-5 and ace-7. These six acetate genes are scattered all over the linkage map of N. crassa. The ace-2 gene was located between pro-1 and com on the right arm of linkage group III. The ace-3 gene was located between al-1 and nic-1 on the right arm of linkage group I. The ace-4 gene was located between cys-10 and fi on the left arm of linkage group IV. The ace-5 gene was located between am and ure-1 on the right arm of linkage group V. The ace-7 gene was located between nic-2 and cr-1 on the right arm of linkage group I.

Do the tightly linked structural genes for nitrate and nitrite reductases in Aspergillus nidulans form an operon? Evidence from an insertional translocation which separates them

Previous work (Rand and Arst, 1977) led to the proposal that the nis-5 mutation results in a new low activity promoter for niiA, the structural gene for nitrite reductase in Aspergillus nidulans. Expression of niiA via this promoter differs from expression of niiA via its normal promoter/initiator in that expression by the new promoter is not subject to nitrate induction or ammonium repression. nis-5 reduces but does not abolish niiA expression mediated by the normal promoter/initiator. In this work we show that nis-5 is associated with and is probably identical to a non-reciprocal translocation in which a considerable portion of the centromere proximal region of the right arm of linkage group II is inserted into linkage group VIII between niiA and niaD, the tightly linked, probably contiguous structural genes for nitrate reductase. This implies that niiA, along with its normal promots yet unidentified by its normal role. Further, it indicates that niiA is transcribed from the niaD-proximal side. As niiA and niaD are separated by a large number of unrelated genes in nis-5 strains, we can safely conclude that expression of niiA does not occur solely by synthesis of a messenger which carries a niaD as well as a niiA transcript. Clearly, niiA and niaD do not form an operon for which a di- (or poly-) cistronic messenger by the only transcript. This is consistent with other experimental evidence which shows that the syntheses of nitrate and nitrite reductases are not coordinately regulated. Nevertheless, all of these data would also be consistent with a model in which niiA and niaD form an operon-type structure having overlapping transcripts, one being di- (or poly-) cistronic and including both niiA and niaD and another being monocistronic for niiA. The reduced niiA expression mediated by the normal promoter/initiator in nis-5 strains could be a consequence of the functioning or positioning of the new linkage group II niiA promoter. An alternative, but not mutually exclusive, explanation would be that the insertional translocation prevents synthesis of a niiA niaD dicistronic transcript so that only that component of niiA expression which is due to a monocistronic niiA messenger can be induced by nitrate (and nitrite) in nis-5 strains. The apparently low activity of the new linkage group II promoter in comparison to the normal niiA promoter/initiator might betoken considerable efficiency of the latter rather than any particular lack of efficiency of the former. In addition, this work has involved extensive new mapping in linkage group II, including both mitotic mapping of the centromere and meiotic mapping of previously unlocated markers. A series of crosses in cluding genotype combinations both heterozygous and homozygous for nis-5 has been used to map the break-points and orientation of the translocation. As one break-point is closer to the centromere of linkage group II than the most centromere proximal identified gene on the same (i.e...

Regulation of phosphate metabolism in Neurospora crassa: identification of the structural gene for repressible acid phosphatase.

A mutant of Neurospora crassa with an altered repressible acid phosphatase has been isolated. The enzyme is much more thermolabile than that of wild type, and has an increased Michaelis constant. Tests of allelic interactions (in partial diploids) and in vitro mixing experiments were consistent with the mutation being in the structural gene for the enzyme. This gene, pho-3, was found to be located in the right arm of Linkage Group IV (LGIV). Thus, pho-3 and the structural gene for repressible alkaline phosphatase, pho-2 (LG V), map in separate linkage groups and cannot be part of the same operon. Neither of these structural genes is linked to the known regulatory genes, nuc-1 (LG I), nuc-2 (LG II), and preg (LG II).

Genetic and enzymatic analysis of a glycerol kinase deficient mutant in Neurospora crassa

Genetic analysis showed that the glycerol non-utilizing isolate gly-u(234) of Neurospora crassa is derived by mutation in a nuclear gene situated in the right arm of linkage group I, about 2.2 cross-over units distal to ad-9 and 11 units proximal to nit-1. Enzymatic testings using a radiochemical method indicate that the mutant is deficient for the enzyme glycerol kinase. The radiochemical testings further indicate that the mutation has inactivated an inducible glycerol kinase, while a low residual activity may be due to a second, basal and non-inducible glycerol kinase, in accordance with a proposal by North (1973, 1974) that Neurospora has two glycerol kinases with these properties.

A perithecial color mutant of Neurospora crassa.

A mutation, per-1, was found in N. crassa which caused orange instead of black perithecia when the protoperithecial parent contained the per-1 allele. No effect of per-1 was found on vegetative morphology or nutritional requirements. The per-1 locus was mapped proximal to iv (?6201) in the right arm of linkage group V.

Super suppressors in Neurospora crassa I. Induction, genetic localization and relationship to a missense suppressor.

Genetic analyses have been made to test the feasibility of using coincident reversions to prototrophy of multiple mutants to select super suppressors (ssu) in Neurospora crassa. Of five double-mutant strains examined, only those mutant combinations in which both members had the properties of nonsense mutations did revert coincidently. Forty-eight genetically purified coincident revertants were crossed to the wild type, and each was shown to contain a suppressor mutation. Five super suppressors were examined more thoroughly. Tetrad and random spore analysis was used to demonstrate that each behaved as a single gene in crosses. Two super suppressors, ssu-1 and ssu-4 were localized respectively on the right and left arm of linkage group 7. Two others, ssu-2 and ssu-3, appear to map on the right arm of linkage group 1. The fifth super suppressor mapped, ssu-7, lies between ad-8 and ylo-1 on linkage group 6. One super suppressor, ssu-1, was interesting because it mapped near the location reported for the suppressor of the missense mutant tryp-3(td201) (Yourno and Suskind 1964a). However, no overlap was found in action spectrum of the two suppressors. Tetrad analysis showed the two suppressors were located about 10 map units apart, the missense suppressor being the more distal to the centromere.

Isolation, mapping, and characterization of trehalaseless mutants of Neurospora crassa.

Mutant strains of Neurospora crassa that lack trehalase and are unable to grow on trehalose were isolated, and the gene (tre) was positioned on the right arm of linkage group I. Maltase and beta-galactosidase activities are almost identical in tre(-) strains, whereas that of invertase was reduced by more than half and those of acid phosphatase and amylase were somewhat increased. Heterocaryons between standard and trehalaseless strains yield less than one-tenth the activity of the former. In addition, strains with duplications heterozygous for trehalase produce less than 1% of the activity of the standard strain. An inhibitor of trehalase has been found in tre(-) strains; its sensitivity to heat and proteolysis, and its nondialyzability suggest that this substance is a protein. The mig gene, which determines the rate of migration of trehalase on acrylamide gels, has been shown to be less than 1 map unit away from the tre gene.

A gene controlling the early development of protoperithecium in Neurospora crassa.

A mutation (ff-1) which specifically destroys the ability to develop protoperithecia was found in Neurospora crassa. This mutation causes no change in vegetative morphology. It is located between arg-5 and try-3 on the right arm of linkage group II.

Pyrimidine synthesis in Neurospora crassa: gene-enzyme relationships.

A new series of pyrimidine-requiring mutants of Neurospora has been isolated and all enzymes involved in pyrimidine biosynthesis are represented by at least one mutant. Among these mutants is included a single isolate for a new locus, pyr-6. This mutant is deficient in dihydroorotase (DHOase) and represents the only enzymatic step in orotate synthesis for which no mutant previously had been found. This mutant, which mapped genetically on the right arm of linkage group V, is unlinked to any of the other pyrimidine mutants. The DHOase-deficient mutant is also characterized by an unexpected growth behavior. The pyr-1 locus has been specifically associated with a lack of dihydroorotate dehydrogenase (DHOdehase). Mutants isolated in this series for other pyrimidine loci have been related to previously isolated mutants by allelism, recombination, and accumulation studies.

Genetic studies of urease mutants in Neurospora crassa

Urease-defective mutants, genetic symbol ure, from Neurospora crassa were studied genetically with the use of known markers in crosses. A method was developed for rapid testing of urease activity in cultures from ascospore isolations. Two ure mutants, isolation numbers (9) and (47), respectively, were located in the right arm of linkage group V, approximately 30 crossover units from the centromere. The two ure mutants are at separate loci at a distance of approximately 3 c.o. units. They are separated by the gene am. Recombination between the two ure loci was studied using the closely linked markers am 1 (32213) and hist-1 (C91). A screening procedure was used to select for rare recombinant types from among random ascospores. A 1 ure +: ure − segregation of spore pairs within dissected asci was found in crosses between ure mutants (9) and (47). Mutants from the two ure loci complements to form urease-positive heterokaryons. The urease mutants are designated with a locus and an allele (isolation) numbers as ure-1 (9) and ure-2 (47), respectively, for future use. The results are discussed in relation to other complex gene-enzyme systems in Neurospora.

A new mutation in Neurospora for sensitivity to ultraviolet.

A failure of the dark repair system for UV damage in Neurospora is determined by a single gene (uvs-2) located far out on the right arm of linkage group IV. The mutant gene has no effect on genetic recombination. The study of a heterokaryon between a normal strain and the sensitive mutant reveals that the mutant is recessive. All conidia from the heterokaryon (even those carrying only the sensitive nuclei) contain sufficient product of the wild-type gene to show normal resistance to UV.

Genetic and complementation studies of a new carotenoid mutant of Neurospora crassa.

A spontaneously occurring mutant called "yellow b" has been isolated and mapped on the right arm of linkage group I in Neurospora crassa 0.15 c.o.u. distal to aur and 2 c.o.u. distal to al-2. These three markers complement each other and are involved in the same biosynthetic pathway.