CHARACTERIZATION, CHROMOSOMAL WRAPPING, AND EXPRESSION OF DIFFERENT UBIQUITIN FUSION PROTEIN GENES IN TISSUES FROM CONTROL AND HEAT-SHOCKEDMAIZE SEEDLINGS

Organisms possess at least two multigene families of ubiquitins: the p olyubiquitins, with few to several repeat units, which encode a ubiqui tin monomer, and the ubiquitin fusion (or extension) protein genes, wh ich encode a single ubiquitin monomer and a specific protein. This rep ort provides details about two ubiquitin fusion protein genes in maize referred to as MubG7 (uwo 1) and MubG10 (uwo 2). Each has one nearly identical ubiquitin coding unit fused without an intervening nucleotid e to an unrelated, 237-nucleotide sequence that encodes for a 79 amino acid protein. The derived amino acid sequences of the two fusion prot eins show that they differ by five amino acids (substitution by either a serine or threonine). MubG7 maps to chromosome 8L162 and MubG10 map s to chromosome 1L131. Analyses of the role(s) of these genes in respo nse to heat shock (1 h at 42.5 degrees C) reveal that the level of the se fusion protein mRNAs in the radicles or plumules from 2-day-old see dlings does not change; however, heat shock does cause a marked reduct ion in the accumulation of these same gene-specific mRNAs in the radic les and plumules of 5-day-old seedlings. These data confirm the sugges tion from our earlier work that there is precise modulation, in a gene -specific manner, of the response to developmental as well as environm ental signals.