CLONING, SEQUENCING AND EXPRESSION OF 2 ISOFORMS OF THE MURINE OCT-1 TRANSCRIPTION FACTOR

Oct-1 is a ubiquitously expressed regulatory gene of the POU domain fa mily. The Oct-1 protein binds to the octamer motif present in the cont rol regions of a variety of genes such as the immunoglobulins, histone H2B and snRNAs. To learn about Oct-1 and its possible role in B-cell maturation, we have used oct-2 cDNA to screen a murine pre-B cell, cDN A library. Two cDNA clones were identical in their POU-homeo box DNA b inding domain, but differed in their 3'-region. Whereas one clone (oct -1a) was very similar to its human oct-1 homologue, the other (oct-1b) , contained an additional 72 bp sequence (designated E1) at the serine threonine rich coding region (position 1485 of the human oct-1), and a deletion of another 72 bp sequence (designated E2) downstream (posit ion 1920). These changes preserve the protein reading frame. DNA blot analysis indicates that murine oct-1 is a single copy gene and that th e two oct-1 isoforms are generated by alternative RNA splicing. RNA bl ots showed that oct-1 is expressed as a large similar to 10 kb transcr ipt in all the cell lines tested. PCR analysis of the El and E2 72 bp regions, indicated the presence of a third isoform containing both E1 and E2 (Oct-1c). Oct-1a and Oct-1b were present in all cell types exam ined, but the level of expression was lower in liver and spleen as com pared to testis, thymus and kidney. The ratio of Oct-1b to Oct-1a rang ed between 0.2 to 0.5, for all tissues examined except for testis whic h expressed higher amounts of oct-1b and/or oct-1c. Our findings thus show that the pattern of expression of the oct-1 gene is more complex than hitherto thought.