Heat Shock Polypeptides Research Articles

Genetic characterization of Coxiella burnetii in Amblyomma varigatum ticks from North-central Nigeria: public health importance

Aim: The purpose of this pilot study was to genetically identify and characterize Coxiella burnetii from Amblyomma varigatum ticks collected on cattle in North central Nigeria. Materials and Methods: A total of 40 partially fed ticks morphologically identified as adult A. variegatum ticks collected from cattle owned by Fulani pastoralists were evaluated for the presence of C. burnetii using PCR, cloning, and sequencing of the heat shock polypeptide gene htpB. Results: C. burnetii DNA was detected in 10 (25%) of the ticks analyzed. Sequences for the C. burnetii gene htpB detected in our samples had 99-100% identity to all other C. burnetii that have been described and that are deposited in the GenBank database. Phylogenetic analysis using neighbor-joining method indicates the clustering of C. burnetii sequences from our study areas with those collected from Oyo state, South-western Nigeria and Spain. Conclusion: This study shows a high infection rate of C. burnetii in A. variegatum ticks in the study areas. Phylogenetic inferences indicates that the strain of C. burnetii found in the North central states of Plateau and Nasarawa were same as those previously reported in the South western state of Oyo. The presence of this pathogen in naturally occurring A. variegatum tick populations could present an additional risk of Q-fever disease to humans, especially to the pastoralists that are closely associated with their animals and are easily exposed to tick bites. Therefore, further studies are needed to assess the competence of A. variegatum ticks as vectors of C. burnetii pathogens.

Induction of expression and co-localization of heat shock polypeptides with the polyalanine expansion mutant of poly(A)-binding protein N1 after chemical stress

Formation of nuclear inclusions consisting of aggregates of a polyalanine expansion mutant of nuclear poly(A)-binding protein (PABPN1) is the hallmark of oculopharyngeal muscular dystrophy (OPMD). OPMD is a late onset autosomal dominant disease. Patients with this disorder exhibit progressive swallowing difficulty and drooping of their eye lids, which starts around the age of 50. Previously we have shown that treatment of cells expressing the mutant PABPN1 with a number of chemicals such as ibuprofen, indomethacin, ZnSO 4, and 8-hydroxy-quinoline induces HSP70 expression and reduces PABPN1 aggregation. In these studies we have shown that expression of additional HSPs including HSP27, HSP40, and HSP105 were induced in mutant PABPN1 expressing cells following exposure to the chemicals mentioned above. Furthermore, all three additional HSPs were translocated to the nucleus and probably helped to properly fold the mutant PABPN1 by co-localizing with this protein.

Heat-stress induced synthesis of chloroplast protein synthesis elongation factor (EF-Tu) in a heat-tolerant maize line

A heat-tolerant maize (Zea mays L.) line, ZPBL 1304, synthesizes a unique set of five heat-shock polypeptides of 45 kDa. Previous studies suggested that these polypeptides might play a role in the development of thermotolerance in maize (Ristic et al., 1996, J. Plant Physiol. 149:424-432; Ristic et al., 1998, J. Plant Physiol. 153:497-505). In the present study, we isolated these polypeptides, sequenced them, and investigated their subcellular distribution and origin. Of the five polypeptides of 45 kDa, three polypeptides, including the two most abundant ones, yielded amino acid sequences similar to the chloroplast and bacterial protein synthesis elongation factor (EF-Tu). This was further confirmed using an antibody raised against maize EF-Tu, which showed a very strong reaction with the 45-kDa heatshock protein(s). Studies on subcellular distribution and origin revealed that the 45-kDa polypeptides were localized to the chloroplasts, and were likely of nuclear origin. A full-length maize EF-Tu cDNA (Zmeftu1), previously isolated from the B73 line of maize, was used as a probe for northern blot analysis of RNA extracted from the ZPBL 1304 maize line (the nucleotide and deduced amino acid sequences of Zmeftu1 are 88% identical to the rice EF-Tu sequence). Northern blots showed a 1.85-fold increase in steady-state levels of EF-Tu mRNA during heat stress. An increase in EF-Tu transcript levels during heat stress was accompanied by increased levels of the EF-Tu protein. Isolated chloroplasts from heat-stressed plants also had higher levels of EF-Tu as compared to control chloroplasts. The maize EF-Tu polypeptides showed > 80% sequence similarity with the bacterial EF-Tu, which has recently been shown to function as a molecular chaperone and to play a role in the protection of other proteins from thermal denaturation (Caldas et al., 1998, J. Biol. Chem. 273:11478-11482). It is hypothesized that chloroplast EF-Tu of the ZPBL 1304 maize line plays an important role in the development of thermotolerance.

Two-dimensional Gel Analysis of 45 ku Heat Shock Proteins from a Drought and Heat Resistant Maize Line

Summary In a previous study, Ristic et al. (1991) described a band of heat-shock protein(s) [HSP(s)] of 45 ku (kDa) in the leaf tissue of a drought and heat resistant maize line, ZPBL 1304. This band had not been previously described in the leaves of maize and does not appear to be common in higher plants. It was not known how many polypeptides comprised this 45 ku band, and whether drought stress can induce the synthesis of proteins of 45 ku. The objectives of this study were two fold: 1) to analyze the 45 ku HSP band from leaf tissue of the ZPBL 1304 line using two-dimensional gel electrophoresis (heat-shock polypeptide study), and 2) to investigate the possible synthesis of 45 ku protein(s) in ZPBL 1304 line under dry conditions. For heat-shock polypeptide study, plants were exposed to two environmental stress treatments: soil drying and high temperature (45 °C) and high temperature alone (45 °C). Generally, the pattern of heat shock (HS) polypeptide synthesis under soil drying and high-temperature conditions was similar to that under high temperature conditions. Two dimensional gel electrophoresis revealed three HS polypeptides of 45 ku with isoelectric points (p/) ranging from 5.0 to 5.5 and two HS polypeptides of 46 ku with p/slightly above 5.5. Drought stress alone did not induce the synthesis of proteins of 45 ku. The possible role of the 45/46 ku HSPs in the development of heat resistance is discussed.

Characterisation of chloroplast heat shock proteins in young leaves of C4 monocotyledons

In vivo radiolabeling of chloroplast proteins in grain sorghum (Sorghum bicolor L. cv. Texas 610) leaves and their separation by one‐dimensional electrophoresis revealed at least 6 heat shock proteins (HSPs) between 24 and 94 kDa. of which the 24 kDa protein was the most prominent. All of these chloroplast heat shock proteins were found exclusively in the stroma. The 24 kDa heat shock protein, upon closer examination using two‐dimensional electrophoresis proved to be two similarly‐sized heat shock polypeptides with identical molecular masses and level of radiolahel incorporation, hut slightly different in isoeiectric points, suggesting isomers. Separation of stromal heat shock proteins synthesised in two other C4 monocotyledons (Punicum miliaceum L. and Umchloa panictrides L.) revealed similar putative isomers. each of 24 kDa. Several other, previously unidentified, heat shock proteins between 22 and 38 kDa were also observed in all three species. In P. miliaceum. the most prominent HSP was the pair of 24 kDa proteins, whereas in U. panicoides. it was a group of 35 to 38 kDa HSPs that was most abundant. In vivo chlorophyll fluorescence measurements showed that no sustained impairment to photosynthetic efficiency had occurred for each species after the heat stress regime. However, when cytoplasmic protein synthesis was inhibited during the high temperature treatment, a dramatic decrease was observed in photosynthetic efficiency, suggesting a possible protective role for chloroplast heat shock proteins. It was also shown that a single chloroplast HSP complex of around 380 kDa was observed in the stroma of both 5. bicolor and P. miliaceum leaves in vivo. This was in contrast to the smaller HSP complex (200–265 kDa) observed in previous studies on chloroplast heat shock proteins in Cj species.

Cytokinins modulate stress response genes in isopentenyl transferase‐transfornied Nicotiana plumbaginifolia plants

The effects of transiently elevated cytokinin levels on gene expression following stress were examined in transgenic Nicotiana plumbaginifolia plants. Plants were transformed with a bacterial gene encoding isopentenyl transferase (ipt) cloned behind the heat shock (HS) protein 70 promoter from Drosophila melanogaster. Following a l‐h, 45°C HS of whole plants, the ipt transcript levels in leaves increased 30‐ to 40‐fold. Analysis of in vitro translation products of leaf messenger RNA showed rapid isopentenyl transferase‐dependent changes in gene expression. A subset comprising 1 to 2% of resolvable translation products was specifically up‐regulated in heat shock ipt‐inducible (HS‐ipt) plants. Several cDNA clones were isolated which correspond to mRNAs that are up‐regulated 2‐ to 4‐fold in HS‐ipt plants. Two of the cDNAs encode stress‐related polypeptides. one a member of a class of small heat shock polypeptides (HSP) and the other, a wound‐inducible glycine‐rich protein. Benzylaminopurine feeding experiments show that the HSP transcripts are up‐regulated by other treatments including watering but that cytokinins strongly accelerate or amplify the response. These data are the first to show altered modulation of stress‐induced genes in intact plants transformed with the cytokinin biosynthesis gene ipt.

Detection and quantitation of a rapidly accumulating and predominant 104 kDa heat shock polypeptide in rice

When 5-day-old rice seedlings were subjected to a high temperature stress (45°C), the shoots as well as roots synthesized and accumulated a 104kDa polypeptide within 1–2 h of the imposition of the stress. The higher levelsof this polypeptide persisted for nearly 16 h when the 45°C temperature stress was continued for 24 h or up to 4 h when seedlings were brought to recovery at 28°C after 4 h of 45°C temperature stress. The leaves obtained from mature plants also accumulated the same polypeptide in response to temperature stress. Exposure of seedlings to salinity, desiccation, cold, wounding or exogenous abscisic acid application had no effect on the accumulation of this polypeptide. Importanly, this polypeptide made nearly 0.4% of the total soluble protein fraction. High temperature induced accumulation of this polypeptide was noted to be conserved in three indica and three japonica cultivars Oryza sativa tested in this study.

Glutamine and glutamate metabolism in normal and heat shock conditions in Drosophila Kc cells: conditions supporting glutamine synthesis maximize heat shock polypeptide expression.

We have previously reported that Drosophila Kc cells require glutamine for maximal expression of heat shock proteins in stressed conditions (Sanders and Kon: J. Cell. Physiol. 146:180-190, 1991). The mechanism of this effect has been investigated by comparing the metabolic utilization of glutamine in conditions which support hsp expression with that of glutamate in conditions where up to 100-fold less hsp is synthesized. This comparison showed that free ammonia was generated by cells incubated in the presence of glutamine in 37 degrees C (heat shock) conditions, but not at 25 degrees C, and not in the presence of glutamate in either normal or heat shock conditions. There was no difference in the amount of [14C]O2 generated from either [14C]-labeled amino acid in the tricarboxylic acid cycle, but three- to four-fold more alanine was synthesized in cells incubated in glutamine than in glutamate. Treating the cells with aminotransferase inhibitors to artificially increase NH3 release raised hsp expression in the presence of glutamate to maximal levels characteristic of glutamine. This potentiation correlated with inhibition of alanine aminotransferase. Since only NH3 production correlated with hsp expression in heat shock conditions in the presence of glutamine, and NH3 addition to glutamate also resulted in maximal hsp expression, we measured glutamine production in glutamate plus NH3 and observed net glutamine synthesis. The supposition that glutamine itself is responsible for the regulatory changes supporting maximal hsp expression was supported by the finding that the glutamine analog, 6-diazo-5-oxo-L-norleucine (DON), mimicked the effects of glutamine. We conclude that glutamine imposes regulatory changes which alter nitrogen metabolism and support hsp expression in Kc cells.

The characterization of the heat-shock response in the arctic plant Saxifraga cernua

A rapid increase in the incubation temperature of whole leaves of the arctic plant Saxifraga cernua, grown at 10 or 20 °C, resulted in the noncoordinate expression of 21 novel and (or) enhanced heat-shock polypeptides. Unlike other organisms, the expression of most of the normal polypeptides was not reduced. Incorporation of radioactivity during hyperthermic shifts was similar in both groups of plants at all temperatures investigated, with peak incorporation recorded at 33 °C. The temperature at which the expression of the heat-shock polypeptides was at a maximum level was also 33 °C. Protein synthesis was reduced after a heat shock at 35 °C and completely inhibited at 38 °C. These data suggest that the preshock growth temperature had no effect on the temperature of maximum expression of the heat-shock polypeptides nor the level of protein synthesis during heat shock. Recovery at 10 °C from a 33 °C heat shock was complete within 7–9 h. Extended time periods (up to 24 h) at the shock temperature of 33 °C demonstrated that the heat-shock response in this arctic plant was multiphasic, consisting of an early group and five sets of late heat-shock polypeptides

A novel set of heat shock polypeptides in malpighian tubules ofDrosophila melanogaster

In contrast to the general notion of induction of a common set of heat shock polypeptides (HSP) in all cell types, heat shocked malpighian tubules (MT) ofDrosophila melanogaster larvae did not synthesize the common set of HSP induced in salivary glands or brain ganglia of larvae and in gonads (testis or ovary) of adult flies. Instead, heat shocked MT of late 3rd instar larvae and freshly eclosed adults synthesized a novel set of polypeptides (MT-specific HSP) with a major induced band at 58 kd. Surprisingly, the MT of older flies synthesized both the MT-specific as well as the common set of HSP in response to heat shock. Fusion genes with hsp70 or hsp26 promoter linked to the lac-Z (beta galactosidase) or to ADH (alcohol dehydrogenase) reporter gene were also not induced in larval MT but showed good induction in the MT of older flies. This unexpected finding raises intriguing issues regarding the nature of MT-specific HSP, their genes and the cell type dependent induction of the two sets of HSP.

Differential Regulation of Closely Related Members of thehsp16Gene Family inCaenorhabditis elegans

The heat-inducible genes encoding 16-kD heat shock polypeptides in Caenorhabditis elegans are found at two separate loci, one containing the 16-1 and 16-48 genes (locus A), and the other, the 16-2 and 16-41 genes (locus B). Despite the highly conserved structures of these genes and their promoters, the B locus produces up to sevenfold more mRNA during heat induction than does the A locus. Since there are two copies of the 16-1 and 16-48 genes at the A locus, the discrepancy in mRNA production is actually as high as 14:1 on a per gene basis. Measurements of the rate of hsp16 mRNA decay during recovery from a heat shock suggest that this difference is not caused by differential mRNA stability; furthermore, nuclear runon experiments yield rates of transcription for the 16-1/48 locus that are approximately threefold higher than those from the 16-2/41 locus. The higher levels of mRNA from the 16-2/41 locus, particularly at longer induction times, seem to be due to a marked difference in the temporal pattern of mRNA production from the two loci. While both loci are transiently activated by a heat shock, the 16-1 and 16-48 genes of the A locus are down-regulated to a lower transcription rate sooner than the genes from the B locus.

Heat-shock response in a tropical Chironomus: seasonal variation in response and the effect of developmental stage and tissue type on heat shock protein synthesis

Examination of heat shock induced transcriptional activity in salivary gland polytene nuclei of a tropical Chironomus, C. striatipennis, revealed nine heat-shock puffs. In 24 °C-reared larvae optimal heat-shock response was seen at 39 °C, while a 41 °C shock was nearly lethal. In a population grown under natural conditions of seasonal variations, the heat-shock response was dependent upon the current ambient temperature. In summer months, response to 39 °C was variable, from complete to no induction of heat-shock puffs in different cells. In control glands from larvae growing at 33–36 °C in summer, heat-shock genes were not active, although in 24 °C-reared larvae, 33 °C already caused partial induction. Unlike the 24 °C-reared population, a 41 °C shock to summer larvae was not lethal. [35S]Methionine-labelled protein synthesis pattern in the summer larvae revealed appreciable accumulation of heat-shock polypeptides in control glands, which possibly autoregulates their further induction and also explains the better thermotolerance of these larvae. In a developmental study of a 24 °C-reared population, some heat-shock polypeptides were found to be commonly synthesized at 39 °C in all the tissues (salivary glands of larvae; Malpighian tubules of larvae, pupae, and adult; adult ovaries), while other heat-shock polypeptides showed apparent tissue and (or) developmental stage specificity. Heat shock protein 70 was most abundantly synthesized in all the tissues examined.Key words: temperature shock, thermotolerance, heat-shock polypeptides, polytene chromosomes, puffs.

Heat Shock Protein Synthesis Induced by Methomyl in Maize (Zea mays L.) Seedlings

Exposure of plumules of intact maize seedlings (Zea mays L.) to S-methyl-N-[(methylcarbamoyl)-oxy]thioacetimidate (methomyl) represses synthesis of several polypeptides normally made under control conditions and induces synthesis of polypeptides similar to maize heat shock polypeptides (HSPs). Three of the methomyl-induced polypeptides (18 kilodaltons) are recognized by antibodies raised against 18 kilodalton maize heat shock polypeptides.

Heat shock response in ovarian nurse cells ofAnopheles stephensi

Transcriptional and translational changes following temperature shock at 37, 39 or 41°C to ovarian cells of Anopheles stephensi were studied. Temperature shock at 39°C induced 6 puffs on polytene chromosomes in the nurse cells as revealed by ( 3 H) uridine incorporation studies. Only the 2R-19B puff was induced at 37°C and was found to be a major temperature shock locus remaining most active at all the 3 temperatures tested. Other temperature shock loci were activated only at 39°C. There was progressive inhibi tion of general chromosomal transcription with the rise of temperature. Transcription was drastically inhibited at 41°C but all the temperature shock loci still remained relatively active. Examination of ( 35 S)methionine labelled newly synthesized ovarian proteins using sodium dodecyl sulphate-polyacrylamide slab gels revealed that all the heat shock poly- peptides except the HSP 70 were synthesized in ovarian cells even at control temperature (29°C). Temperature shock induced the synthesis of HSP 70 and elevated the levels of other heat shock polypeptides (82, 30, 29, 23 and 17 KD). Present results suggest that the threshold level for induction of a complete heat shock response in mosquitos is higher (39°C) than the other dipteran insects studied and that a 41°C treatment is not lethal as in the case of Drosophila, Chironomus etc. These features reflect the adaptations of mosquitos to tropical climate and their dietary habit of warm blood meal.

Elevated serine catabolism is associated with the heat shock response in Escherichia coli

The biochemical events associated with the heat shock response are not well understood in any organism, nor have the signals that initiate the induction of heat shock protein synthesis been identified. In this work, we demonstrate that the rate of serine catabolism of Escherichia coli cells grown in glucose minimal medium supplemented with serine is elevated three- to sevenfold when the growth temperature is shifted from 37 to 44 degrees C. Elevations in growth temperature and mutations or treatments that lead to elevated basal rates of serine catabolism at 37 degrees C result in the excretion into the culture medium of acetate derived from exogenous serine. Increases in the basal level of serine catabolism at 37 degrees C do not per se induce a heat shock response but are associated with abnormalities in the pattern of induction of heat shock polypeptides following a temperature shift. We postulate that the events responsible for or resulting from the elevation in serine catabolism associated with a shift-up in temperature modulate the induction of 3 of the 17 heat shock polypeptides identified in E. coli. These observations suggest that heat shock diverts serine away from the production of glycine and C1 units, which are required for initiation of protein synthesis and for nucleotide biosynthesis, and towards acetyl coenzyme A and acetate.

Characterization of the heat-shock response in spinach (Spinacia oleracea L.)

Spinach (Spinacia oleracea L. cultivar Longstanding Bloomsdale) grown at 20 °C was subjected to a range of rapid thermal shifts as high as 42 °C. There was a decrease in the level of protein synthesis following heat-shock treatments above 34 °C as indicated by the level of incorporation of L-[35S]methionine. In vivo labelled polypeptides and in vitro translation products of RNA isolated from leaf tissue and analyzed using one-dimensional sodium dodecyl sulfate polyacrylamide gel electrophoresis and fluorography, indicated that the temperature of induction of all 15 heat-shock proteins in the 20 °C grown plants was 36 °C. In addition, heat-shock RNA was coordinately expressed and the translation of heat-shock proteins was noncoordinate with respect to temperature. Treatment with cycloheximide and with chloramphenicol demonstrated that heat-shock protein synthesis in spinach was restricted to cytosolic ribosomes. Synthesis of some low molecular weight heat-shock proteins were insensitive to actinomycin D, suggesting greater stability of these heat-shock RNAs. The heat-shock polypeptide profile of plants grown at 10 °C was similar to that of plants grown at 20 °C, with 14 heat-shock proteins being induced at 36 °C. The growth temperature did not influence the final array of heat-shock proteins synthesized nor alter the temperature of induction of the heat-shock response.Key words: heat-shock response, heat-shock proteins, Spinacia oleracea.

Correlation between the activity of a 5,6-dichloro-1-β-D-ribofuranosylbenzimidazole-insensitive puff and the synthesis of major heat-shock polypeptide, hsp70, in Chironomus thummi

The induction of puff III-A3b, a major heat-shock puff in Chironomus thummi salivary cells, was insensitive to the transcription inhibitor 5,6-dichloro-1-beta-D-ribofuranosylbenzimidazole (DRB), whereas no transcriptional activity could be detected at the other heat-shock puffs in the presence of this drug. In these conditions, a polypeptide with the same Mr and isoform pattern as those of the major heat-shock polypeptide, hsp70, was synthesized. These results suggest that hsp70 is encoded by locus III-A3b. In addition to DRB insensitivity, incorporation of [3H]UTP on puff III-A3b took place in an in vitro transcription assay under low-salt conditions (100 mM NaCl); no labelling could be detected at the other heat-shock puffs under these conditions. Although DRB has been reported as a specific inhibitor of RNA polymerase II-directed transcription, and although the low-salt conditions were not propitious for the activity of this enzyme, RNA polymerase II was detected on puff III-A3b and on the other heat-shock puffs by immunofluorescence with anti-RNA polymerase II antibodies.

Major sclerotial polypeptides of psychrophilic fungi: temperature regulation of in vivo synthesis in vegetative hyphae

Western blot analysis of the major sclerotial polypeptides of the psychrophilic species Myriosclerotinia borealis (W51) and Coprinus psychromorbidus (LRS131) indicated that these polypeptides were not present in vegetative hyphae during growth at permissive temperature (5 °C), but significant accumulations were observed in hyphae upon prolonged exposure to nonpermissive temperature (25 °C). In contrast, low levels of sclerotial polypeptides were detected in the vegetative hyphae of Typhula incarnata (W29) and Typhula idahoensis (W21). We show, for the first time, that the in vivo synthesis of the major sclerotial polypeptides was induced when vegetative hyphae of M. borealis and C. psychromorbidus were shifted from 5 to 10 °C for 12 h. In contrast, vegetative hyphae of T. idahoensis and T. incarnata appeared to synthesize low levels of sclerotial polypeptides constitutively at 5 °C. Furthermore, a shift from 5 to 10 °C had little effect on the synthesis of major sclerotial polypeptides in the Typhula species. Prior exposure of vegetative hyphae from all species to 25 °C for 2 days caused a marked reduction in the capacity to synthesize sclerotial polypeptides. However, vegetative hyphae of T. incarnata synthesized a new polypeptide of 35 kDa that had not been detected previously. Antiserum to low molecular mass maize heat-shock polypeptides cross reacted with the major sclerotial polypeptides of T. idahoensis only. We conclude that the more psychrophilic species examined, M. borealis (W51) and C. psychromorbidus (LRS131), exhibit temperature-induced synthesis and accumulation of sclerotial polypeptides in vegetative hyphae. In contrast, sclerotial polypeptides of the less psychrophilic Typhula species appear to be expressed constitutively in vegetative hyphae.

Gene expression in chick morula.

The polypeptides synthesized during the morula stage in the chick embryo are insensitive to transcriptional inhibition by α-amanitin. Protein synthesis seems to depend predominantely, if not exclusively, on the recruitment of maternal mRNA, rather than on embryonic gene expression in chick morula. The morula embryo expresses the heatshock polypeptides when stressed at 43°C. The heat-induced polypeptides are isoforms of polypeptides that are synthesized normally. These polypeptides are α-amanitin sensitive and appear to mark the first major expression of the embryonic genome in the chick embryo.

Aging results in an unusual expression of Drosophila heat shock proteins.

We used high-resolution two-dimensional polyacrylamide gel electrophoresis to evaluate the effect of aging on the heat shock response in Drosophila melanogaster. Although the aging process is not well understood at the molecular level, recent observations suggest that quantitative changes in gene expression occur as these fruit flies approach senescence. Such genetic alterations are in accord with our present data, which clearly show marked differences in the synthesis of heat shock proteins between young and old fruit flies. In 10-day-old flies, a heat shock of 20 min results in the expression of 14 new proteins as detectable by two-dimensional electrophoresis of [35S]methionine-labeled polypeptides, whereas identical treatment of 45-day-old flies leads to the expression of at least 50 new or highly up-regulated proteins. In addition, there is also a concomitant increase in the rate of synthesis of a number of the normal proteins in the older animals. Microdensitometric determinations of the low molecular weight heat shock polypeptides on autoradiographs of five age groups revealed that their maximum expression occurs at 47 days for a population of flies with a mean life span of 33.7 days. Moreover, a heat shock effect similar to that observed in senescent flies occurs in young flies fed canavanine, an arginine analogue, before heat shock.