In testis mRNA stability and translation initiation are extensively under the 
control of poly(A)-binding proteins (PABP). Here we have cloned a new human 
testis-specific PABP (PABP3) of 631 amino acids (70.1 kDa) with 92.5% identical 
residues to the ubiquitous PABP1. A northern blot of multiple human tissues 
hybridised with PABP3- and PABP1-specific oligonucleotide probes revealed two 
PABP3 mRNAs (2.1 and 2.5 kb) detected only in testis, whereas PABP1 mRNA (3.2 
kb) was present in all tested tissues. In human adult testis, PABP3 mRNA 
expression was restricted to round spermatids, whereas PABP1 was expressed in 
these cells as well as in pachytene spermatocytes. PABP3-specific antibodies 
identified a protein of 70 kDa in human testis extracts. This protein binds 
poly(A) with a slightly lower affinity as compared to PABP1. The human PABP3 
gene is intronless with a transcription start site 61 nt upstream from the 
initiation codon. A sequence of 256 bp upstream from the transcription start 
site drives the promoter activity of PABP3 and its tissue-specific expression. 
The expression of PABP3 might be a way to bypass PABP1 translational repression 
and to produce the amount of PABP needed for active mRNA translation in 
spermatids.