Background: Terminal deoxynucleotidyltransferase (TdT) is a DNA polymerase
that enhances Ig and TcR gene diversity in the N region in B- and T-cells.
TdT is found as a member of a large protein complex in the lysate of the th
ymocytes. To elucidate the molecular mechanism of the synthesis of the N re
gion, we first attempted to isolate the genes with products that are intera
cting directly with TdT.
Results: Using a yeast two-hybrid system, we isolated a cDNA clone encoding
a novel nuclear protein that interacts with TdT. This protein was designat
ed as TdT interacting factor 1 (TdIF1). TdIF1 has a high degree of homology
to the transcription factor p65, which belongs to the nuclear receptor sup
erfamily. TdIF1 contains HMG-1 and HMG-Y DNA binding domains (AT-hooks) and
can bind to single- and double-stranded DNA. TdT and TdIF1 were co-eluted
at position 232 kDa by gel filtration of MOLT4 lysate. TdIF1 can enhance Td
T activity fourfold in vitro assay system using oligo(dT)(16) as primers.
Conclusions: TdIF1 binds directly to TdT, both in vitro and in vivo. TdIF1
and TdT exist as the members of a 232 kDa protein complex. TdIF1 can enhanc
e TdT activity maximum fourfold in vitro assay system, suggesting that it p
ositively regulates the synthesis of the N region during V(D)J recombinatio
n in the Ig and TcR genes.