Size heterogeneity of ribosomal RNA in eukaryote evolution--1. rRNA molecular weights in species containing intact large ribosomal subunit RNA.

1. The molecular weights of the two major rRNA species (L-rRNA, large ribosomal subunit RNA, and S-rRNA, small ribosomal subunit RNA) of a variety of deuterostomia, green plants and fungi have been investigated by gel electrophoresis in 99% formamide, pH 9; the overall pattern obtained under these conditions differs to some extent from that deduced by electrophoresis in neutral-salt solutions. 2. The molecular weights of the deuterostomian S-rRNA species have been conserved at a value of 0.65 X 10(6), whereas those of the L-rRNA have been kept at 1.40 X 10(6) in the lower species but have increased to 1.55 X 10(6) in birds and to 1.65 X 10(6) in mammals. 3. The molecular weights of the L-rRNA and S-rRNA components of the green plants (Dycotyledons, Monocotyledons and Gymnosperms) have been generally conserved at 1.30 X 10(6) and 0.65 X 10(6). 4. The molecular weight of the L-rRNA of the fungi has been conserved at 1.36-1.38 X 10(6), being 0.1 X 10(6) daltons heavier than that of the plants; the S-rRNA exhibits a limited degree of variability, ranging between 0.65 X 10(6) and 0.72 X 10(6).