cDNA for rat
transcription factor IIIA (
TFIIIA) was cloned by degenerate PCR and rapid amplification of
cDNA ends. This
cDNA coded for a
protein with nine Cys(2)His(2) zinc fingers and a non-finger C-terminal tail; 63%
amino acid (aa) sequence identity was observed with the Xenopus
TFIIIA zinc finger region. Recombinant rat
protein containing only the nine fingers afforded
DNase I protection of the identical
nucleotides protected by Xenopus laevis native
TFIIIA on the Xenopus 5S
RNA gene internal control region. A putative mouse
TFIIIA clone was identified in an expressed sequence tag database by sequence similarity to rat
TFIIIA. Recombinant nine-finger
protein from this clone afforded
DNase I protection of the Xenopus
5S rRNA gene like the native frog
protein as did a recombinant nine-finger form of a putative human
TFIIIA clone. These
DNA binding results demonstrate that these clones code for the respective mammalian TFIIIAs. Rodent and human TFIIIAs share about 87% aa sequence identity in their zinc finger regions and have evolved to about the same extent as X. laevis and Xenopus borealis TFIIIAs. A
monoclonal antibody against human p53
tumor suppressor bound to rat and mouse
TFIIIA but not to human
TFIIIA in Western blots. The N-terminal regions of rodent and human
TFIIIA do not contain the oocyte-specific initiating Met and accompanying conserved residues found in fish and amphibian TFIIIAs. In their non-finger C-terminal tails, mammalian and amphibian TFIIIAs share a conserved transcription activation domain as well as conserved nuclear localization and
nuclear export signals.