A protein binding to CArG box motifs and to single-stranded DNA functions as a transcriptional repressor.
A CArG box motif [CC(A+T-rich)6GG] is one of the DNA elements required for muscle-specific gene transcription. Nuclear factors in mouse C2 myogenic cells strongly bind to the CArG box in the first intron of the gene (Sm alpha-A) encoding human smooth muscle alpha-actin. To clone cDNAs of the CArG box-binding factor (CBF), lambda gt11 cDNA expression libraries from C2 cells were screened for in situ DNA binding specific for this CArG box sequence. The 1.6-kb cDNA (CBF-A) encoding 285 amino acids (aa) was obtained, and a beta-galactosidase fusion protein, bacterially produced from the cDNA, bound to DNA fragments containing several CArG boxes. When the expression level of CBF-A in C2 cells increased by transfection of CBF-A expression plasmids, Sm alpha-A transcription was repressed. The deduced aa sequence of CBF-A is similar to some single-stranded (ss) nucleic acid-binding proteins. The fusion protein could bind to ssDNA, whereas CBF in C2 cell nuclear extracts could not. From these results, CBF-A is a novel CArG box-, ssDNA- and RNA-binding protein, as well as a repressive transcriptional factor.
Kamada
S
S
Department of Oncogene Research, Osaka University, Japan.
Miwa
T
T
D000199:Actins / Q000235:genetics; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002460:Cell Line; D017124:Conserved Sequence; D004277:DNA, Single-Stranded / Q000235:genetics / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D034481:Heterogeneous-Nuclear Ribonucleoprotein Group A-B; D051379:Mice; D008969:Molecular Sequence Data; D009132:Muscles / Q000166:cytology / Q000378:metabolism*; D012045:Regulatory Sequences, Nucleic Acid; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism*; D013045:Species Specificity
D000199:Actins; D004277:DNA, Single-Stranded; D004268:DNA-Binding Proteins; D034481:Heterogeneous-Nuclear Ribonucleoprotein Group A-B; D012097:Repressor Proteins; C077048:Hnrnpab protein, mouse