Mk. Shirra et al., ONE EXON OF THE HUMAN LSF GENE INCLUDES CONSERVED REGIONS INVOLVED INNOVEL DNA-BINDING AND DIMERIZATION MOTIFS, Molecular and cellular biology, 14(8), 1994, pp. 5076-5087
The transcription factor LSF, identified as a HeLa protein that binds
the simian virus 40 late promoter, recognizes direct repeats with a ce
nter-to-center spacing of 10 bp. The characterization of two human cDN
As, representing alternatively spliced mRNAs, provides insight into th
e unusual DNA-binding and oligomerization properties of LSF. The seque
nce of the full-length LSF is identical to that of the transcription f
actors alpha CP2 and LBP-1c and has similarity to the Drosophila trans
cription Factor Elf-1/NTF-1. Using an epitope-counting method, we show
that LSF binds DNA as a homodimer. LSF-ID, which is identical to LBP-
1d, contains an in-frame internal deletion of 51 amino acids resulting
from alternative mRNA splicing. Unlike LSF, LSF-ID did not bind LSF D
NA-binding sites. Furthermore, LSF-ID did not affect the binding of LS
F to DNA, suggesting that the two proteins do not interact. Of three s
hort regions with a high degree of homology between LSF and Elf-1/NTF-
1, LSF-ID lacks two, which are predicted to form P-strands. Double ami
no acid substitutions in each of these regions eliminated specific DNA
-binding activity, similarly to the LSF-ID deletion. The dimerization
potential of these mutants was measured both by the ability to inhibit
the binding of LSF to DNA and by direct protein-protein interaction s
tudies. Mutations in one homology region, but not the other, functiona
lly eliminated dimerization.