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

U1 small nuclear RNA (U1 snRNA) is encoded by a large family of genes (30-125 copies/haploid genome) which are transcribed by RNA polymerase II. U1 snRNA is thought to function in gene splicing. Since the U1 genes were found to be greater than 20 kb apart by analyzing genomic phage clones, the chromosomal location of U1 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 U1-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 U1 fragments segregated with the chromosome 1 markers peptidase C and adenylate kinase 2. All other chromosomes showed greater than or equal to 19% discordancy . An additional 13 karyotyped cell hybrids, analyzed by Southern filter analysis, confirmed the assignment of this class of U1 genes to chromosome 1. Additional digests with MspI and PstI indicated that most U1 genes are located on chromosome 1. To determine if the U1 RNAs are located predominantly at one site or dispersed over chromosome 1, a tritium-labeled U1 probe was hybridized in situ to metaphase chromosomes. The majority of the grains were at band 1p36 .3, suggesting that most of the U1 genes are located in this region.