CHARACTERIZATION OF THE POLYUBIQUITIN GENE IN THE MARINE RED ALGA GRACILARIA-VERRUCOSA

We have cloned a nuclear gene (UB16R) and corresponding cDNAs that enc ode polyubiquitin in the florideophycidean red alga Gracilaria verruco sa. The gene encodes a polyubiquitin composed of six tandem ubiquitin units, followed by a single glutamine residue. The deduced amino acid sequences are identical among all six units, and identical to the ubiq uitin of the florideophyte Aglaothamnion neglectum. There is high sequ ence similarity among the red algal ubiquitins and those of animals, g reen plants, fungi and several protists. Only one polyubiquitin gene w as found by Southern hybridization analysis of G. verrucosa nuclear DN A. The upstream region of the gene is rich in putative cis-acting tran scription-regulatory elements, including a putative heat-responsive el ement. Poly(A) addition to UB16R mRNA was observed in cDNAs at four di fferent sites, implicating the sequences AATAAA and (or) AGTAAA as pol y(A) addition signals. The polyubiquitin genes of red algae show featu res of concerted evolution, but appear to be subject to less sequence homogenization than those of animals.