Characterization of novel hsp70 in mammalian cells

A new protein detected in heat resistant mutants of a murine fibrosarcoma has been identified as a member of the hsp70 family. The protein is similar to the constitutive hsp70 of the parent cells with regard to its antibody cross-reactivity, its ability to bind to an ATP affinity column and partial amino acid sequencing. It is present in addition to, and in similar amounts to, the constitutive isoform of the heat resistant mutant cells and the parent cell line. The lack of either of two post-translational modifications common to other hsps, phosphorylation and ADP-ribosylation, and the demonstration of mRNA for the novel protein suggest that it is a separate gene product and not a post-translational modification of the constitutive hsp70. To our knowledge, this protein has not been described in other systems and may be important in the expression of the heat resistant phenotype of these cells. The in vivo phosphorylation patterns also show that hsp90 and hsp28 are heavily phosphorylated in the heat resistant mutant, but that two other stress proteins reported to be phosphorylated under some conditions are not phosphorylated in these cells.