COMPARATIVE-ANALYSIS OF BIP GENE-EXPRESSION IN MAIZE ENDOSPERM

Binding protein (BiP) is the endoplasmic reticulum member of the highl y conserved HSP70 (heat shock protein 70) family of molecular chaperon es. We have isolated and characterized two different BiP cDNA clones c orresponding to genes expressed in immature kernels. These two cDNAs s hare extensive sequence similarity but map to unlinked loci in the mai ze genome. A comparison of the aa sequences predicted from the cDNA cl ones revealed only six aa differences between them. Investigation of g ene-specifc expression was carried out by RNA gel blot analysis. RNAs corresponding to both cDNA clones were present in increased amounts in the endosperm of floury-2 (fl2), Mucronate (Mc) and Defective endospe rm-B30 (De-B30) maize mutants, which produce abnormal storage protein s. Similar increases in RNAs corresponding to both probes were detecte d in cells treated with either of two agents that interfere with prote in folding, azetidine-2-carboxylic acid (AZC) and tunicamycin. Investi gation of the genomic complexity of the BiP genes by Southern blot ana lysis revealed several cross-hybridizing bands. These results are sugg estive that the BiP genes expressed in endosperm are coordinately regu lated members of a more complex maize BiP multigene family. (C) 1997 E lsevier Science B.V.