Polyadenylation is a process of endonucleolytic cleavage of the mRNA, followed 
by addition of up to 250 adenosine residues to the 3' end of the mRNA. 
Polyadenylation is essential for eukaryotic mRNA expression, and CstF-64 is a 
subunit of the CstF polyadenylation factor that is required for accurate 
polyadenylation. We discovered that there are two forms of the CstF-64 protein 
in mammalian male germ cells, one of which (CstF-64) is expressed in all 
tissues, the other of which (tauCstF-64) is expressed only in male germ cells 
and in brain (albeit at significantly lower levels in the brain). Therefore, we 
were surprised to find that, using reverse transcription-PCR, cDNA cloning, and 
RNA blot analyses, tauCstF-64 mRNA was expressed at higher levels in brain than 
in testis. Also, tauCstF-64 mRNA was expressed at lower but detectable levels in 
all tissues tested, including epididymis, heart, kidney, liver, lung, muscle, 
ovary, spleen, thymus, and uterus. These results suggest the hypothesis that 
tauCstF-64 mRNA is regulated at the translational or post-translational level.