The ribosomes of Drosophila. III. RNA and protein homology between D. melanogaster and D. virilis

Species-specific proteins of the 50S subunit of the chloroplast ribosome in the genus Nicotiana

The large subunits (50S) of chloroplast ribosomes were isolated from Nicotiana tabacum, a species of the Western Hemisphere, and from N. excelsior and N. gossei, Australian species. Their proteins were compared by two-dimensional gel electrophoresis. A pair of proteins (T12 and T12) observed in N. tabacum has electrophoretic mobilities which differ from those of a similarly migrating, and probably homologous, pair of proteins observed in N. excelsior and N. gossei. The species-specific proteins in N. tabacum differ slightly in electrophoretic mobilities based on both charge and molecular weight from those in N. excelsior and N. gossei. Tryptic digests of radioiodinated proteins reveal that the peptide maps of all six proteins are similar. These results suggest that chemically altered forms of one or more proteins of the 50S chloroplast ribosome subunit may exist in vivo.

Characterization of the ribosomal proteins from mosquito (Aedes albopictus) cells

Proteins from the large and small subunits of Aedes albopictus (mosquito) cytoplasmic ribosomes were characterized by two-dimensional polyacrylamide gel electrophoresis. The small subunit contained 28-31 proteins ranging in molecular mass from 10 to 49 kDa. The large subunit contained 36-39 proteins that ranged in molecular mass from 11 to 53 kDa. The largest protein on the small subunit, S1, was the predominant phosphorylated ribosomal protein. Under long-term labelling conditions, L4 and L33 were also phosphorylated. Peptide mapping by partial proteolysis indicated that Ae. albopictus S1 may share partial amino acid homology with the phosphorylated ribosomal protein S6 from Drosophila melanogaster. Unlike Drosophila S6, however, Aedes S1 was not dephosphorylated during heat shock. Treatment of mosquito cells with the insect molting hormone 20-hydroxyecdysone did not affect phosphorylation of ribosomal proteins.

Developmental and evolutionary comparisons of proteins from purified ribosomal subunits in two silkmoths

Developmental comparisons of silkmoth ribosomal proteins were performed by parallel two-dimensional electrophoretic analyses of proteins derived from developing adult wings and from ovarian follicles at the prechoriogenic and choriogenic stages of development (before and during secretion of the chorion, respectively). Proteins of 40S and 60S subunits were prepared and analyzed separately. A single major developmental difference was observed, exclusively in choriogenic follicles: the majority of a 40S subunit protein, S6, was shifted to a more acidic form, possibly as a result of phosphorylation. A less prominent change was apparently due to quantitative variation between two forms of one large subunit protein. The developmental comparisons were performed in two species of the genus Antheraea, with consistent results. Comparisons between the two species revealed remarkable evolutionary conservation of the ribosomal protein patterns, sharply contrasting with the evolutionary diversification of chorion structural proteins in the same two species. The only detectable interspecies differences in ribosomal components were (a) slightly more acidic behaviour of one small-subunit protein and more basic behaviour of one large-subunit protein in Antheraea polyphemus as compared to Antheraea pernyi, and (b) presence of an apparently species-specific 60 S subunit protein in A. pernyi, which in A. polyphemus probably co-migrates with a neighbouring protein.

Studies of ribosomal proteins of yeast species and their hybrids: gel electrophoresis and immunochemical cross-reactions

The cytoplasmic ribosomal proteins (r-proteins) of seventeen yeast species of the genera Saccharomyces and Kluyveromyces were analyzed by one-dimensional gradient polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulphate. The electrophoretic patterns of cytoplasmic r-proteins from different species display extensive differences in both the 40S and the 60S subunit. Relatedness of species suggested by r-protein patterns correlates well with that based on DNA/DNA homology (Bicknell and Douglas 1970). Immunochemical cross-reactions and antibiotic susceptibility tests were also used to compare different species. Analyses of r-proteins from two different interspecific hybrids showed that their ribosomes were hybrid, containing r-proteins from both parents. These findings are discussed in relation to the evolution of yeast species and the regulation of expression of r-proteins in eucaryotes.

Evoluation of Drosophila mitochondrial DNAs. Analysis of heteroduplex molecules

We have mapped the single block of non-homologous sequences and measured the extent and distribution of base-pair substitutions within the homologous sequences in Drosophila melanogaster: Drosophila virilis heteroduplex mitochondrial DNAs (mtDNAs). Of the 4.8 kilobases long, unusually (A + T)-rich region in D. melanogaster mtDNA, only 0.5 kilobases can react with related, but not identical sequences in D. virilis mtDNA, while the rest (4.3 kilobases in the long arm of a heteroduplex loop) is replaced by a shorter, non-homologous region (1.0 kilobases in the short arm of the loop). No additional heterologous regions are evident. Homologous sequences have accumulated on the average 15.5% base-pair changes. Regionally, these substitutions are relatively uniformly distributed (14.5--16.5%) except for a single, more conserved region (10--13%), which presumably represents the ribosomal cistrons. The lack of general sequence stability suggests that the invariant topographic organization of the nucleotide sequence, previously recognized among Drosophila mtDNAs, is under more stringent selection than the sequence per se.

Comparative study between prokaryotes and eukaryotes by chemical iodination of ribosomal proteins

Escherichia coli and Saccharomyces cerevisiae ribosomal proteins were chemically iodinated with 125I by chloramine T under conditions in which the proteins were denatured. The labelled proteins were subsequently separated by two-dimensional gel electrophoresis with an excess of untreated ribosomal proteins from the same species. The iodination did not change the electrophoretic mobility of the proteins as shown by the pattern of spots in the stained gel slabs and their autoradiography. The 125I radioactivity incorporated in the proteins was estimated by cutting out the gel spots from the two-dimensional electrophoresis gel slabs. The highest content of 125I was found in the ribosomal proteins L2, L11, L13, L20/S12, S4 and S9 from E. coli, and L2/L3, L4/L6/S7, L5, L19/L20, L22/S17, L29/S27, L35/L37 and S14/S15 from S. cerevisiae. Comparisons between the electrophoretic patterns of E. coli and S. cerevisiae ribosomal proteins were carried out by coelectrophoresis of labelled and unlabelled proteins from both species. E. coli ribosomal proteins L5, L11, L20, S2, S3 and S15/S16 were found to overlap with L15, L11/L16, L36/L37, S3, S10 and S33 from S. cerevisiae, respectively. Similar coelectrophoresis of E. coli 125I-labelled proteins with unlabelled rat liver and wheat germ ribosomal proteins showed the former to overlap with proteins L1, L11, L14, L16, L19, L20 and the latter with L2, L5, L6, L15, L17 from E. coli.