An mRNA encoding poly-ubiquitin in porcine corpus luteum: identification by cDNA cloning and sequencing

A cDNA library derived from a particular fraction of mRNA of porcine corpus luteum was screened by hybrid-release. cDNA clone pCL208 selected an mRNA which, in cell-free translation, directed the synthesis of a major polypeptide of 28 kD. Sequence analysis of clone pCL208 revealed that the entire coding sequence contained three complete repeats and a fourth incomplete repeat of porcine ubiquitin, joined head-to-tail without any spacer peptide sequences. The ultimate ubiquitin molecule contained a Phe residue as a carboxy-terminal extension. The coding sequence terminated with the stop codon TAA followed by a short untranslated region, the polyadenylation signal AATAAA, and a tract of A residues. Northern analysis indicated the presence of two types of ubiquitin-specific mRNAs, i.e., 1100 and 2500 bp, in porcine corpus luteum.