Xy. Zhang et al., INCREASING BINDING OF A TRANSCRIPTION FACTOR IMMEDIATELY DOWNSTREAM OF THE CAP SITE OF A CYTOMEGALOVIRUS GENE REPRESSES EXPRESSION, Nucleic acids research, 23(15), 1995, pp. 3026-3033
A closely related family of ubiquitous DNA binding proteins, called MD
BP, binds with high affinity to two 14 base pair (bp) sites within the
human cytomegalovirus immediate early gene 1 (CMV IE1) enhancer and w
ith low affinity to one site beginning 5 bp downstream of the CMV IE1
transcription start point (+5 site). Unlike several cap position downs
tream MDBP sites in mammalian genes, these MDBP sites do not require c
ytosine methylation for optimal binding, Mutation of one of the enhanc
er MDBP sites to prevent MDBP recognition modestly increased the funct
ion of a neighboring CREB binding site in a transient transfection ass
ay in the context of one promoter construct, A much larger effect on r
eporter gene expression (a 10-fold reduction) was seen when the low af
finity MDBP recognition sequence at position +5 was converted to a hig
h affinity site in a plasmid containing the CMV IE1 promoter upstream
of the reporter gene, Evidence that the increased binding of MDBP at t
he mutant site is largely responsible for the observed results was pro
vided by transfection experiments with this high affinity MDBP +5 site
re-mutated to a non-binding site and by in vitro transcription assays
.