Effect of sequence differences between somatic and oocyte 5S RNA genes on transcriptional efficiency in an oocyte S150 extract.

The differential expression of the Xenopus laevis somatic and oocyte 5S RNA genes is partially, but not solely, due to several base differences near the 5' boundary of the internal control region. A hybrid oocyte 5S gene with somatic-type base changes at +47, +53, +55, and +56 had intermediate transcriptional activity in oocyte S150 extracts. These base substitutions also resulted in increased affinity for a factor(s), other than TFIIIA, which forms a stable complex with the 5S gene.