Identification of mRNAs encoding low molecular mass heat-shock proteins in maize (Zea mays L.)
Subjecting 5-day-old maize seedlings to a rapid elevation in growth temperature (heat shock; 25–42 °C) results in a shift in the pattern of protein synthesis in maize plumules from the production of a broad spectrum of proteins to the new and (or) enhanced synthesis of a small number of heat-shock proteins (HSPs). The low relative molecular mass (Mr) HSPs, and more specifically an 18-kDa HSP with four major isoelectric variants, represent the majority of HSP synthesis following cell-free translation of total cellular poly (A)+ RNAs and polyribosomal RNAs extracted from heat-shocked plumules. Immunochemical studies, using polyclonal antibodies raised against the 18-kDa HSPs, show that the 18-kDa HSPs synthesized in vitro share immunochemical properties with HSPs of the same Mr synthesized in vivo by heat-shocked plumules. Furthermore, size fractionation and translation analyses of total cellular poly(A)+ RNAs extracted from heat-shocked plumules demonstrate that poly(A)+ RNAs encoding an 18-kDa HSP(s) have an estimated size of 0.6–0.95 kilobases. The observation that 18-kDa HSPs are absent among the translation products and immunoprecipitates of proteins synthesized in vitro by RNAs extracted from control plumules (25 °C) suggests that the mRNAs encoding 18-kDa HSPs are heat-shock induced.Key words: mRNA, maize, heat shock.