Interaction of two DNA-binding factors expressed in B- and T-lymphocyte precursors.

Two DNA-binding factors detected in pre-B and pre-T cells and absent from mature lymphocytes are described. Factor A displayed no appreciable sequence selectivity but bound only to DNA fragments longer than 120 base pairs. The minimal size of a binding site was lower on an intrinsically curved DNA, suggesting formation of tertiary structures on DNA. Factor B interacted with sequences, other than consensus recombination signals, present in the vicinity of unrearranged immunoglobulin genes. Binding of factor B inhibited the interaction of factor A with the same DNA fragment. The presence of the factor-B-binding site in an episomal V(D)J recombinase substrate lowered the frequency of recombination in vivo. We propose that the two factors described here may function as accessory proteins in V(D)J recombination, possibly modulating accessibility of genes to the recombinase.