Structure and polymorphism of ribosomal RNA genes in the marine shrimp Penaeus vannamei

We have examined the structure and polymorphism of the genes that encode ribosomal RNA in the Pacific whiteleg shrimp, Penaeus vannamei. We have found that the rRNA genes are polymorphic within and between individual shrimp and between selectively bred families. The polymorphism suggests the presence of repeated DNA sequence elements in the intergenic spacer region upstream from the promoter for transcription of the rRNA genes. In other organisms, such repeated elements have been shown to serve as alternative promoters or enhancers for transcription. If the same is true in P. vannamei, the observed polymorphism might be linked to traits important for shrimp aquaculture.