An N-terminally fused Xenopus transcription factor IIIA synthesized in Escherichia coli is biologically active.

A 1.5-kilobase DNA fragment containing the Xenopus transcription factor IIIA (TFIIIA) gene was inserted into the prokaryotic expression vector pIN-III(A) containing the lpp/lac promoter. The recombinant DNA was introduced into Escherichia coli K-12 strain SB221. The expression TFIIIA gene was induced by isopropyl-beta-D-thiogalactopyranoside, which resulted in the synthesis of a recombinant TFIIIA with an extra 17 amino acids fused to its N terminus as predicted from the nucleotide sequence. The engineered gene product, purified to at least 90% homogeneity, retained its binding affinity to the intragenic control region of the 5 S RNA gene, as well as its activity to stimulate 5 S RNA gene transcription in vitro.