Developmental regulation of the kappa locus involves both positive and negative sequence elements in the 3 ' enhancer that affect synergy with the intron enhancer
Xd. Liu et al., Developmental regulation of the kappa locus involves both positive and negative sequence elements in the 3 ' enhancer that affect synergy with the intron enhancer, J BIOL CHEM, 274(6), 1999, pp. 3285-3293
Expression of the mouse immunoglobulin kappa locus is regulated by the intr
on and 3' enhancers. Previously, we have reported that these enhancers can
synergize at mature B cell stages. Here we present our recent studies on th
e identification and characterization of the 3' enhancer sequences that pla
y important roles in this synergy. By performing mutational analyses with n
ovel reporter constructs, we find that the 5' region of the cAMP response e
lement (CRE), the PU.1/PIP, and the E2A motifs of the 3' enhancer are criti
cal for the synergy. These motifs are known to contribute to the enhancer a
ctivity. However, we also show that mutating other functionally important s
equences has no significant effect on the synergy. Those sequences include
the 3' region of the CRE motif, the BSAP motif, and the region 3' of the E2
A motif. We have further demonstrated that either the 5'-CRE, the PU.1/PIP,
or the E2A motif alone is sufficient to synergize with the intron enhancer
. Moreover, the PU.1 motif appears to act as a negative element at pre-B ce
ll stages but as a positive element at mature B cell stages. We have also i
dentified a novel negative regulatory sequence within the 3' enhancer that
contributes to the regulation of synergy, as well as developmental stage an
d tissue specificity of expression. While the levels of many of the 3' enha
ncer binding factors change very little in cell lines representing differen
t B cell stages, the intron enhancer binding factors significantly increase
at more mature B cell stages.