An analysis of mRNAs for a group of heat shock proteins of soybean using cloned cDNAs.

Abstract

Hybridization studies carried out with poly(A)+ RNA and its corresponding cDNA showed the presence of a new highly abundant RNA class after heat shock (hs) at 40 degrees C in soybean hypocotyl compared to tissue incubated under normal conditions at 28 degrees C. cDNA clones complementary to RNAs of this class were isolated; eleven clones were characterized and used in the analysis of these abundant RNAs. The most abundant hs-sequences were found to be 800-900 nucleotides in length and present in about 19,000 copies per cell. Extensive sequence homology among hs-induced RNAs was indicated by cross-hybridization of cDNA clones and by common protein patterns generated in hybrid release translations. The existence of at least two different nucleotide sequences common to several different hs poly(A)+ mRNAs was documented by different, nonoverlapping protein patterns obtained by in vitro synthesis with hybrid selected RNAs. Four clones contained a sequence common to mRNAs for at least 13 proteins of 15,000-18,000 daltons; another sequence common to mRNA for three to four proteins of 21,000-23,000 daltons was selected by one clone. Two other clones selected a major hs-protein of about 18,000 daltons. The mRNAs of these low molecular weight hs-proteins accumulated rapidly after induction at either 40 degrees C or 42.5 degrees C and decreased rapidly during subsequent incubation at 28 degrees C.