SCYGR5

Two cDNAs and their corresponding genes (GhUBC1 and GhUBC2) encoding ubiquitin-conjugating enzymes (E2s) have been cloned and characterized from allotetraploid cotton Gossypium hirsutum ((AD)(1) genome). Three additional E2 genes (GaUBC1, GtUBC2, and GrUBC2) have also been identified from diploid cottons Gossypium arboreum (A(2) genome), Gossypium thurberi (D(1) genome), and Gossypium raimondii (D(5) genome), respectively. The derived amino acid sequences of the five closely related cotton E2s are 77-79% identical to yeast ScUBC4 and ScUBC5. The GhUBC1/2 gene family is composed of two members, and genomic origin analysis indicates that GhUBC1 and 2 are individually present in the A and D subgenomes of G. hirsutum. The transcript levels of GhUBC1/2 increased significantly in leaves and flowers at senescence, suggesting that GhUBC1/2 may play a role in the degradation of target proteins that function in the delay of the senescence program. Correlated with high auxin content and auxin-associated effects, GhUBC1/2 are also highly expressed in the youngest leaves, the apical part of lateral roots, and elongating fibers. Genetic complementation experiments revealed that GhUBC1 and 2 can substitute for the function of ScUBC4 and 5 required for the selective degradation of abnormal and short-lived proteins in a yeast ubc4ubc5 double mutant.

We have identified a novel factor H-related cDNA, which was isolated from a human liver cDNA library. The DOWN16 clone is 1269 base pairs in size and hybridized to a mRNA of 1.4 kilobases. Similar to the previously described factor H-related proteins, the predicted translation product of 331 amino acids contains a hydrophobic signal sequence followed by a stretch of five short consensus repeats (SCRs). These five SCRs display homology to SCRs of factor H: SCRs1-3 (DOWN16) are homologous to SCRs6-8 of factor H, while SCRs4 and -5 are related to SCRs19 and -20. In vitro translation demonstrated that the DOWN16 cDNA encodes a primary translation product of an apparent molecular mass of 37,500 Da which is directed to the secretory pathway and is glycosylated. Thus, we propose that the protein will be present in human serum. The relatedness of structural elements between this novel gene and factor H may suggest common functions of these proteins not yet determined.