Nucleotide sequence and chromosomal mapping of the 5S rDNA repeat of the crustacean Proasellus coxalis

In this investigation we analysed the 5S rRNA genes of the isopod crustacean Proasellus coxalis. 5S rDNA hybridization of digested genomic DNA and amplification by PCR demonstrate that these genes are organized in tandem repeats of 589 bp, 120 of which represent the coding sequence and 469 the spacer sequence. Proasellus coxalis is the first crustacean species in which 5S rRNA genes have been found tandemly arranged without being linked to other repeated genes. The PCR product has been used as a probe in FISH to locate the 5S rRNA genes on two chromosome pairs of the P. coxalis karyotype. Comparison of the 5S rDNA sequence of this species with previously published sequences of six other crustacean species shows the existence of a good correlation between phylogenetic relationships and sequence identity