Two highly reiterated nucleotide sequences in the low C-value genome of Panagrellus redivivus

Two families of highly reiterated satellite nucleotide (nt) sequences have been found in the genome of the sexually separated nematode Panagrellus redivivus. The repeats are arranged in tandem arrays but the different satellites are not intermingled. Monomeric lengths are of 155 bp for one kind and 167 bp for the other; they were named E155 and E167. The A + T content is elevated in both families (i.e., 59.5%, and 65.3%, respectively). No similarity was found between the two satellites nor to other known highly repetitive elements. Furthermore, nt methylation as well as transcriptional activity were negative. An internal subrepeating unit, about 30 bp long, was observed in E167, implying that it could have evolved from a shorter sequence. Reiteration frequencies are approx. 30,000 and 40,000 copies per haploid genome, for E155 and E167, respectively, constituting together about 17% of the total DNA. This figure is astonishingly high, considering a C-value of 70,000 kb in P. redivivus, which is thought to be the lower limit for metazoans. Hence, the genome complexity is approx. 58,000 kb. In contrast to the nematodes Ascaris lumbricoides and Parascaris equorum, however, P. redivivus does not seem to eliminate large blocks of satellite DNA in the presomatic cells during early development.