Structure and expression of a Xenopus gene encoding an snRNP protein (U1 70K)

A cDNA and two genes for the Xenopus laevis U snRNP 70K protein have been cloned and partially sequenced. The cDNA encodes a protein whose predicted mol. wt is 57 kd but which migrates as a 70 kd protein in SDS-PAGE when translated in vitro from a cDNA transcript. The predicted protein sequences of the human and Xenopus U1 70K are shown to be very similar. Analysis of several genomic clones suggests that there are at least two, and possibly more, different genes coding for the 70K protein in the Xenopus genome. The two genes analysed in detail cover approximately 16 kb and are divided into 10 exons of which the last exon covers more than half of the protein coding sequence. During Xenopus development several different stage-specific RNAs hybridizing to the U1 70K cDNA are detected. The promoter region of one of the cloned genes is demonstrated to be functionally active, and to show apparent differences from other pol II promoters.