Sequences translated by Balbiani ring 75S RNA in vitro are present in giant secretory protein from Chironomus tentans

The total amount of noncoding sequences on chromosomes of contemporary organisms varies significantly from species to species. We propose a hypothesis for the origin of these noncoding sequences that assumes that (a) an -0.55-kilobase (kb)-long reading frame composed the primordial gene and (it) a 20-kb-long single-stranded polynucleotide is the longest molecule (as a genome) that was polymerized at random and without a specific template in the primordial soup/cell. The statistical distribution of stop codons allows examination of the probability of generating reading frames of =0.55 kb in this primordial polynucleotide. This analysis reveals that with three stop codons, a run of at least 0.55-kb equivalent length of nonstop codons would occur in 4.6% of 20-kb-long polynucleotide molecules. We attempt to estimate the total amount of noncoding sequences that would be present on the chromosomes of contemporary species assuming that present-day chromosomes retain the prototype primordial genome structure. Theoretical estimates thus obtained for most eukaryotes do not differ significantly from those reported for these specific organisms, with only a few exceptions. Furthermore, analysis of possible stop-codon distributions suggests that life on earth would not exist, at least in its present form, had two or four stop codons been selected early in evolution.

Section: Possible Length Of a Primordial Genementioning

confidence: 99%

Origin of noncoding DNA sequences: molecular fossils of genome evolution.

Naora¹,

Miyahara²,

Curnow³

1987

“…The BR gene-encoded secretory proteins have previously been electrophoretically estimated to have relative molecular masses in the order of 0.8-1 x 106 daltons (10)(11)(12)(13)(14), and length variants consistent with the presence of gene alleles have been observed (38).…”

Section: Resultsmentioning

confidence: 99%

“…It was shown early on that BRs are loci of intense transcription (4,5), and the puffing concept was strongly supported by molecular studies in which the synthesis and transport to polysomes of 37-kilobase-pair (kb) BR gene mRNA transcripts could be established (6)(7)(8)(9). Subsequently, it was shown that BRs encode large secretory proteins with relative molecular masses of -1 x 106 daltons, which, after export, form protein fibers used to spin a larval tube during the aquatic larval period (10)(11)(12)(13)(14).…”

mentioning

confidence: 97%

Sequence organization of the Balbiani ring 2.1 gene in Chironomus tentans.

Wieslander¹,

Paulsson²

1992

“…The large BRs (BR1 and BR2) produce giant messengers (3,4) and code for giant secretory polypeptides, sp-Ia and sp-Ib (5,6). If larvae are raised in solutions with monosaccharides or some other compounds, including glycerol, a BR6 develops from a condensed band and BR2 regresses (7,8).…”

mentioning

confidence: 99%

“…6 min. Glands were processed and chromatographed on a Sepharose 6B column (5). An aliquot of 300 ,ud of the pooled peak fractions (3 ml) containing sp-I was run on Bio-Gel P2 column to change to 0.05 M Tris HCl buffer, pH 7.2.…”

mentioning

confidence: 99%

Balbiani ring induction in phosphate metabolism

Galler¹,

Rydlander²,

Riedel³

et al. 1984

Self Cite

Balbiani rings (BR), giant puffs in Chironomus larval salivary glands, code for giant secretory proteins. As shown earlier, the normally dominant BR2 is turned off with its putative translation product during exposure of larvae to compounds that diminish the stores of Pi. A BR6 develops from a compact chromosome band, and a new giant protein appears in the secretion as the major component. We have determined the sequence of cloned DNA fragments representative for large parts of BR1 and BR2 (normally active) and the inducible BR6. There is an excess of positive charges and high contents of serine/threonine in the coded amino acid composition for the BR1 and BR2 sequences. The coded amino acid sequence for the BR6 clone shares homologies with the others but has an excess of negative charges and lacks serine/threonine. This suggested that the Pi effects observed earlier could be related to differences in phosphorylation between the normal proteins and the BR6 product. This could be confirmed by measurements of phosphorylation, which occurs in the normal giant proteins mainly at seryl residues. P export with giant secretory protein is normally quantitatively important. Thus, BR6 activation should decrease P loss when Pi pools are lowered because of inducer action.Balbiani rings (BR) in polytene chromosomes of salivary glands from Chironomus larvae are genetic determinants of secretory proteins (1,2). The large BRs (BR1 and BR2) produce giant messengers (3, 4) and code for giant secretory polypeptides, sp-Ia and sp-Ib (5, 6). If larvae are raised in solutions with monosaccharides or some other compounds, including glycerol, a BR6 develops from a condensed band and BR2 regresses (7,8). Simultaneously a new giant protein appears (sp-Ic), immunologically different from sp-Ia and spIb, and the labeling of sp-Ib decreases (8). A new giant RNA species also shows up, similar in size to the RNA from BR1 and BR2 (75S RNA) (9). The sp-Ic may account for 25% to more than 50% of the total gland incorporation of methionine (ref. 8 and this paper). Pi decreases in the hemolymph in response to inducers, and addition of Pi to the inducing solution abolishes the action. The induction also can be reversed with Pi (9).In order to relate the Pi effects to the properties of the genes, we have cloned short fragments of BR1, BR2, and BR6 representing considerable parts of the genes (15-20 kb). The base sequences of these fragments suggested that phosphorylation might occur in the normal polypeptides, sp-Ia and sp-Ib, but not in sp-Ic. Direct analyses confirmed that suggestion. Because the P content in sp-Ia and sp-Ib is high and secretory protein export is quantitatively important, the switch to sp-Ic (BR6) implies that P is saved when, because of inducers, the Pi pool is low. MATERIALS AND METHODSAnimals. Mid-fourth-larval instar Chironomus pallidivittatus animals were used, raised as described for Chironomus tentans (10). For squashes, animals from single egg-string cultures were used; for other experiments, animals from mass cu...