A set of heptapeptides was used to compare the relative peptide affini
ties of three proteins of the hsp70 family: bacterial DnaK, mammalian
cytosolic hsc70, and BiP from mammalian ER. Each hsp displays a charac
teristic pattern of relative affinities. DnaK and hsc70 are more simil
ar to each other than to BiP. A difference in peptide binding specific
ity may be an important determinant in adjusting an hsp70 family membe
r to its particular cellular function.