Members of the USF family of helix-loop-helix proteins bind DNA as homo- as well as heterodimers.
We have isolated human cDNA clones for USF2, a new member of the upstream stimulatory factor (USF) family of transcription factors. Analysis of these clones revealed the existence of highly conserved elements in the C terminal region of all USF proteins. These include the basic region, helix-loop-helix (HLH) motif, and, in the case of the human proteins, the C-terminal leucine repeat (LR). In addition, a highly conserved USF-specific domain is located immediately upstream of the basic region. Using in vitro translated proteins, we found that all members of the USF family bound DNA as dimers. The N-terminal portion of USF, including the USF-specific domain, was entirely dispensable for dimer formation and DNA-binding. However, deletion mutants of USF2 lacking the LR were deficient in DNA-binding activity. Interestingly, each of the USF proteins could form functional heterodimers with the other family members, including the sea urchin USF, which does not have a LR motif. This indicates that the conserved LR in human USF is not required for dimer formation, and influences only indirectly DNA-binding.
Sirito
M
M
Department of Molecular Genetics, University of Texas M.D. Anderson Cancer Center, Houston 77030.
Walker
S
S
Lin
Q
Q
Kozlowski
M T
MT
Klein
W H
WH
Sawadogo
M
M
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D004247:DNA / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000235:genetics* / Q000378:metabolism; D015870:Gene Expression; D005796:Genes; D006367:HeLa Cells; D006801:Humans; D008969:Molecular Sequence Data; D005810:Multigene Family; D011487:Protein Conformation; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D014157:Transcription Factors / Q000235:genetics* / Q000378:metabolism; D051720:Upstream Stimulatory Factors
D004268:DNA-Binding Proteins; D011993:Recombinant Fusion Proteins; D014157:Transcription Factors; C497181:USF1 protein, human; C497184:USF2 protein, human; D051720:Upstream Stimulatory Factors; D004247:DNA