We present the sequence of the 26S rRNA of the yeast Saccharomyces carlsbergensis as inferred from the gene sequence. The molecule is 3393 nucleotides long and consists of 48% G+C; 30 of the 43 methyl groups can be located in the sequence. Starting from the recently proposed structure of E. coli 23S rRNA (see ref. 25) we constructed a secondary structure model for yeast 26S rRNA. This structure is composed of 7 domains closed by long-range base pairings as n the bacterial counterpart. Most domains show considerable conservation of the overall structure; unpaired regions show extended sequence homology and the base-paired regions contain many compensating base pair changes. The extra length of the yeast molecule is due to a number of insertions in most of the domains, particularly in domain II. Domain VI, which is extremely conserved, is probably part of the ribosomal A site. alpha-Sarcin, which apparently inhibits the EF-1 dependent binding of aminoacyl-tRNA, causes a cleavage between position 3025 and 3026 in a conserved loop structure, just outside domain VI. Nearly all of the located methyl groups, like in E. coli, are present in domain II, V and VI and clustered to a certain extent mainly in regions with a strongly conserved primary structure. The only three methyl groups of 26S rRNA which are introduced relatively late during the processing are found in single stranded loops in domain VI very close to positions which have been shown in E. coli 23S rRNA to be at the interface of the ribosome.

Deletion analysis of artificial rRNA minigenes transformed into Saccharomyces cerevisiae revealed that a 110 bp long fragment corresponding to positions ‐36 to +74 relative to the 3′‐end of the 26S rRNA gene, is both necessary and sufficient for obtaining transcripts whose 3′‐termini are identical to those of 26S and 37S (pre‐)rRNA. These termini are produced via processing of longer transcripts because in an rna 82.1 mutant the majority of the minigene transcripts extend further downstream. Since the rna 82.1 mutation inactivates an endonuclease involved in the 3′‐processing of 5S pre‐rRNA it is concluded that the maturation of 37S‐ and that of 5S pre‐rRNA requires a common factor. Comparison of the spacer sequences between Saccharomyces carlsbergensis, Saccharomyces rosei and Hansenula wingei revealed several conserved sequence blocks within the region between +10 and +55. These conserved sequence tracts, which are part of a longer region showing dyad symmetry, are supposed to be involved in the interaction with the processing component(s). Deletion of the sequences required for the formation of the 3′‐ends of 26S rRNA and 37S pre‐rRNA revealed a putative terminator for transcription by RNA polymerase I situated at position +210. This site maps within a DNA fragment that also contains the enhancing element for rDNA transcription by RNA polymerase I.

Insulin and related peptides are key hormonal integrators of growth and metabolism in vertebrates. There is little biochemical evidence for insulin-related peptides in invertebrates, apart from insects for which definitive structural information on these peptides (prothoracicotropic hormone, PTTH) has recently been obtained. We report here the first complete complementary DNA-derived primary structure of a preproinsulin-related protein from identified neurons in an invertebrate, the mollusc Lymnaea stagnalis. We have demonstrated by in situ hybridization that transcription of the gene for this molluscan insulin-related peptide (MIP) occurs in the cerebral light-green cells, giant neuroendocrine cells involved in the control of growth, as well as in a pair of neuroendocrine cells called the canopy cells. The insulin-related peptide precursor has the same overall structure as its vertebrate counterparts. The discovery of insulin-related peptides in invertebrates substantiates the evidence for a widespread and early evolutionary origin of the insulin superfamily.

No abstract

The sequences of the nontranscribed spacers (NTS) of cloned ribosomal DNA (rDNA) units from both Saccharomyces cerevisiae and Saccharomyces carlsbergensis were determined. The NTS sequences of both species were found to be 93% homologous. The major disparities comprise different frequencies of reiteration of short tracts of six to sixteen basepairs. Most of these reiterations are found within the 1100 basepairs long NTS between the 3'-ends of 26S and 5S rRNA (NTS1). The NTS between the starts of 5S rRNA and 37S pre-rRNA (NTS2) comprises about 1250 basepairs. The first 800 basepairs of NTS NTS2 (adjacent to the 5S rRNA gene) are virtually identical in both strains whereas a variable region is present at about 250 basepairs upstream of the RNA polymerase A transcription start. In contrast to the situation in Drosophila and Xenopus no reiterations of the putative RNA polymerase A promoter are present within the yeast NTS. The strands of the yeast NTS reveal a remarkable bias of G and C-residues. Yeast rDNA was previously shown to contain a sequence capable of autonomous replication (ARS) (Szostak, J.W. and Wu, R (1979), Plasmid 2, 536-554). This ARS, which may correspond to a chromosomal origin of replication, was located on a fragment of 570 basepairs within NTS2.