The small nuclear ribonucleoproteins, SmB and B', are products of a single gene.

Nucleotide sequencing of HeLa genomic DNA amplified by the polymerase chain reaction revealed 696-bp and 841-bp introns within the gene encoding the proteins SmB and SmB', respectively. Since splice consensus sequences were observed flanking the 145-bp insertion detected in the cDNA encoding SmB, we conclude that SmB and SmB' are derived from alternative splicing of a single gene transcript.