Structure of a processed gene of mouse cytoplasmic gamma-actin transposed into a BAM5 sequence: insertion has created 13 base-pair direct repeats.

We have cloned a processed gene related to cytoplasmic gamma-actin from a phage library of mouse brain DNA. The gene lacks introns, carries a poly(dA) tract of 19-base pairs at the 3' end and is flanked by 13-base-pair direct repeats. Southern blotting experiments indicated that this segment is embedded in highly repetitive and strongly methylated sequences. Direct comparison of the flanking sequences with those of mouse repetitive DNAs revealed that this processed gene is integrated into a BAM5 family, which is one of the repetitive sequences of the mouse genome. In addition, it was shown that the direct repeats were created by a duplication of the corresponding 13-bp stretch of the BAM5 DNA as a consequence of the integration of this segment. These results strongly suggest that the processed gamma-actin gene has been conveyed to this locus through a poly(A)+ RNA intermediate by a transposon-like mechanism.