Promoter analysis of the human ubiquitin-conjugating enzyme gene family UBE2L1-4, including UBE2L3 which encodes UbcH7

Abstract

UbcH7 is a ubiquitin-conjugating enzyme mediating c-fos degradation, transcription factor NF-kappaB maturation, human papilloma virus-mediated p53 and Myc protein degradation, in vitro. Previously, we characterised a highly dispersed gene family, UBE2L1-UBE2L4, whose members could potentially encode different isoforms of the UbcH7 protein. UBE2L3, located at chromosome 22q11.2, is the only identified family member with introns and encodes a polypeptide sequence identical to that of UbcH7. Promoter characterisation of UBE2L1, UBE2L3 and UBE2L4 5'-upstream regions was performed to establish which are transcribed under normal physiological conditions and after heat shock. Promoter activity was observed only with the UBE2L3 construct, the minimal promoter lying within a region 100 bp upstream of the transcriptional start site. No evidence for the presence of UBE2L1 or UBE2L4 transcripts was observed in human or murine tissues and cell lines. These data strongly suggest that UBE2L1 and UBE2L4 are likely to encode pseudogenes. Sequencing revealed that the UBE2L3 promoter contained no TATA or CCAAT boxes. Protein:DNA interaction studies confirmed the presence of binding sites for the transcription factors AP2 and Sp1 in the UBE2L3 minimal promoter. Deletion of these binding sites indicated that these factors are crucial for transcription of this gene.