Localization of human U1 small nuclear RNA genes to band p36.3 of chromosome 1 by in situ hybridization

Ul small nuclear RNA (Ul snRNA) is encoded by a large family of genes (30-125 copies/haploid genome) which are transcribed by RNA polymerase II. Ul snRNA is thought to function in gene splicing. Since the Ul genes were found to be >20 kb apart by analyzing genomic phage clones, the chromosomal location of Ul genes in the human genome was determined using Southern filter analysis of DNA isolated from human-rodent somatic cell hybrids and by in situ hybridization. Human DNA digested with PvuII and probed with a Ul-specific probe, pD2, show several major hybridizing fragments. Of these, two human PvuII fragments of 1.4 kb and 2.4 kb had unique mobilities compared to mouse fragments. In a study of 19 cell hybrids, the human-specific Ul fragments segregated with the chromosome 1 markers peptidase C and adenylate kinase 2. All other chromosomes showed>-19% discordancy. An additional 13 karyotyped cell hybrids, analyzed by Southern filter analysis, confirmed the assignment of this class of Ul genes to chromosome 1. Additional digests with MspI and PstI indicated that most Ul genes are located on chromosome 1. To determine if the Ul RNAs are located predominantly at one site or dispersed over chromosome 1, a tritium-labeled Ul probe was hybridized in situ to metaphase chromosomes. The majority of the grains were at band 1p36.3, suggesting that most of the Ul genes are located in this region.