Mapping of polysomal messenger RNA and heterogeneous nuclear RNA to the lightly staining G-bands of human chromosomes

The observation that ¹²⁵I-labeled polysomal mRNA is located in lightly staining regions confirms the previous finding with cDNA transcribed from total cytoplasmic poly(A+) RNA and strongly suggests that genes present in low multiplicity copies are primarily located in G-negative rather than G-positive bands. This should serve as a useful guide in the mapping of individual genes to specific chromosomal bands. The finding that reiterated large-molecular-weight nuclear RNA sequence transcripts are also localized in lightly staining regions supports the suggestion that mRNA and HnRNA originate from related DNA sequences.