Molecular cloning and analysis of DNA complementary to three mouse Mr = 68,000 heat shock protein mRNAs

The construction and isolation of three recombinant DNAs complementary to different mouse L-cell Mr = 68,000 heat shock protein (hsp68) mRNAs is described. cDNA libraries derived from heat-shocked mouse L-cell poly(A)+ RNA by the vector-linked primer strategy of cDNA synthesis and cloning of Okayama and Berg (Okayama, H., and Berg, P. (1982) Mol. Cell. Biol. 2, 161-170) were screened first with a Drosophila hsp70 heterologous probe and subsequently with a cDNA probe isolated from the first screening. Positive clones were assigned to one of three sets based on their restriction map, and the largest member of each group was chosen for further analysis. All three cDNAs hybrid-select mRNA for the mouse major heat shock protein (hsp68) as assayed by in vitro translation and hybridize preferentially to two heat shock-induced hsp68 mRNAs on Northern blots. The coding regions of the cDNAs are almost identical and closely resemble other HSP70 genes but the 3' untranslated regions diverge considerably. Differences in the lengths of the untranslated regions are responsible for the two different sized induced hsp68 mRNAs in mouse L-cells. The physical maps of these cDNA clones and the limited number of mouse genomic DNA fragments detected on Southern blots suggest that there are at least three closely related heat shock-inducible members of the mouse HSP70 gene family. None of the cloned cDNAs are derived from the two related cognate genes known to be present in the mouse genome.