Ascorbate-dependent expression of ubiquitin genes in guinea pigs

In an attempt to characterize gene(s), of which the expression is ascorbate-dependent, a cDNA fragment encoding ubiquitin was isolated from a subtracted cDNA library constructed from spleen RNAs of ascorbate-deficicent or -replete guinea pigs. On Northern blot analysis, three transcripts (1.8 kb ubiX, 1.3 kb ubiY and 0.7 kb ubiZ) were detected. The ubiY encodes four direct repents of tile 76 amino acid ubiquitin sequence with seven additional amino acids, V-Y-A-S-P-I-F, at the C-terminus. The transcript ubiX appears to comprise more than five repents of the ubiquitin-encoding unit. The ubiZ encodes a ubiquitin monomer fused to an 80 amino acid extension exhibiting 100% amino acid sequence identity to the human homolog, HUMUBA80R. The ubiX gene was expressed animal-dependently. The ubiY mRNA levels decreased under ascorbate-deficient conditions, and increased under ascorbate-replete conditions, whereas ubiZ mRNA remained unaltered at low levels under the feeding conditions used here.