NONRANDOM GENE ORGANIZATION - STRUCTURAL ARRANGEMENTS OF SPECIFIC PRE-MESSENGER-RNA TRANSCRIPTION AND SPLICING WITH SC-35 DOMAINS

This work demonstrates a highly nonrandom distribution of specific gen es relative to nuclear domains enriched in splicing factors and poly(A )(+) RNA, and provides evidence for the direct involvement of these in pre-mRNA metabolism. As investigated in hundreds of diploid fibroblas ts, human collagen I alpha 1 and beta-actin DNA/RNA showed a very high degree of spatial association with SC-35 domains, whereas three nontr anscribed genes, myosin heavy chain, neurotensin, and albumin, showed no such preferential association. Collagen I alpha 1 RNA accumulates w ithin the more central region of the domain, whereas beta-actin RNA lo calizes at the periphery. A novel approach revealed that collagen RNA tracks are polarized, with the entire gene at one end, on the edge of the domain, and the RNA extending into the domain. Intron 26 is splice d within the RNA track at the domain periphery. Transcriptional inhibi tion studies show both the structure of the domain and the gene's rela tionship to it are not dependent upon the continued presence of accumu lated collagen RNA, and that domains remaining after inhibition are no t just storage sites. Results support a model reconciling light and el ectron microscopic observations which proposes that transcription of s ome specific genes occurs at the border of domains, which may also fun ction in the assembly or distribution of RNA metabolic components. In contrast to the apparently random dispersal of total undefined hnRNA s ynthesis through interdomain space, transcription and splicing for som e genes occurs preferentially at specific sites, and a high degree of individual pre-mRNA metabolism is compartmentalized with discrete SC-3 5 domains.