The
hsp70A gene (referred to previously as the
hsp70 class A gene) is both a heat inducible and a developmentally expressed
hsp70 gene. Sequencing of the
hsp70A gene has been completed in an effort to determine the similarities to a Drosophila heat inducible
hsp70 gene ( Ingolia, et. al., Cell 21, 669 (1980)) and to a developmentally expressed, or cognate,
hsp70 gene (
hsc4; M. Slater and E.A. Craig, pers. commun.) which is also induced upon heat shock. We have found: (1) At the 5' region of the
hsp70A gene, there are three heat shock elements (HSE; Pelham, Cell 30, 517 (1982)). (2) Within the transcribed region, there are a total of three introns (IS1, 49 bp; IS2 194 bp; IS3, 55 bp). (3) At the 3' end of the gene, there appears to be a second, overlapping gene which has transcription and translation starts before the polyA addition site for the
hsp70A gene. (4) The
hsp70A amino acid sequence exhibits more homology with the
hsc4 protein (79%) than with the heat inducible protein (71%). (5) There is more homology of the carboxy terminus of the
hsp70A amino acid sequence with the
hsc4 amino acid sequence than with the heat inducible
hsp70 amino acid sequence. The carboxy terminus appears to 'define' the type of function for each
hsp70 gene. The
hsp70A gene is expressed at high levels during development and its expression is increased two to six fold higher upon heat shock. The
hsp70A mRNA appears to be the major
hsp70 mRNA during both development and heat shock (T. Snutch, Ph.D. Thesis, Simon Fraser University, 1984). The
hsc4 gene is also expressed at high levels during development and its expression is increased two fold upon heat shock. It is also the major
hsp70 mRNA during development and during heat shock (Palter, et. al., MCB 6, 1187 (1986)). Based upon the amino acid homologies and the similarities in expression, we believe that the
hsp70A gene is analogous to the
hsc4 gene from Drosophila. We predict that mutations of the
hsp70A gene will be one of two types. The first could be lethal due to the lack of an essential
hsp70 protein. The second could be 'temperature sensitive'. That is, a mutation with no effects at low temperatures because the function of the
hsp70A gene would be compensated for by other genes but lethal at higher temperatures when the
hsp70A gene function cannot be compensated for. The
hsp70A gene has been mapped to the right arm of LGIV approximately 0.1 mu to the left of
dpy-4 ( Snutch, et. al., submitted) using RFLDs. A search for mutations in this area will be done to define alleles of
hsp70A.