INTRAGENOMIC POLYMORPHISM OF RIBOSOMAL-RNA GENES IN HUMAN-CHROMOSOME-13

Screening of cosmid library of human chromosome 13 revealed that the b ulk of mini- and microsatellite (MS and MCS) sequences is concentrated in the region of ribosomal operon. Cloned rDNA sequences capable of h ybridizing with a GACA probe and with some other MS and MCS variants w ere mapped using oligonucleotide probes complementary to conservative regions of 18S and 28S rRNA genes. The marked intrachromosome polymorp hism of rRNA genes revealed was due to differences in the content and localization of MS and MCS, as well as to point mutations in the trans cribed and spacer regions of the genes. Basing on the data obtained, o ne may hypothesize that there exist regions of more or less pronounced genetic stability within rRNA genes. It appeared that rRNA gene varia nts with numerous point mutations are usually loaded with many MS and MCS sequences as well. Such hypervariable sequences appear not only in spacers but also in the coding, the most conservative rDNA regions.