Constitutive synthesis

Constitutive expression, not a particular primary sequence, is the important feature of the H3 replacement variant hv2 in Tetrahymena thermophila.

Molecular and Cellular Biology ◽

10.1128/mcb.17.11.6303 ◽

1997 ◽

Vol 17 (11) ◽

pp. 6303-6310 ◽

Cited By ~ 37

Author(s):

L Yu ◽

M A Gorovsky

Keyword(s):

Protein Sequence ◽

Tetrahymena Thermophila ◽

Histone H3 ◽

Constitutive Expression ◽

Histone Variants ◽

Wild Type ◽

Ciliated Protozoan ◽

Knockout Mutant ◽

Double Knockout ◽

Constitutive Synthesis

Although quantitatively minor replication-independent (replacement) histone variants have been found in a wide variety of organisms, their functions remain unknown. Like the H3.3 replacement variants of vertebrates, hv2, an H3 variant in the ciliated protozoan Tetrahymena thermophila, is synthesized and deposited in nuclei of nongrowing cells. Although hv2 is clearly an H3.3-like replacement variant by its expression, sequence analysis indicates that it evolved independently of the H3.3 variants of multicellular eukaryotes. This suggested that it is the constitutive synthesis, not the particular protein sequence, of these variants that is important in the function of H3 replacement variants. Here, we demonstrate that the gene (HHT3) encoding hv2 or either gene (HHT1 or HHT2) encoding the abundant major H3 can be completely knocked out in Tetrahymena. Surprisingly, when cells lacking hv2 are starved, a major histone H3 mRNA transcribed by the HHT2 gene, which is synthesized little, if at all, in wild-type nongrowing cells, is easily detectable. Both HHT2 and HHT3 knockout strains show no obvious defect during vegetative growth. In addition, a mutant with the double knockout of HHT1 and HHT3 is viable while the HHT2 HHT3 double-knockout mutant is not. These results argue strongly that cells require a constitutively expressed H3 gene but that the particular sequence being expressed is not critical.

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Putative GTP-binding protein, Gtr1, associated with the function of the Pho84 inorganic phosphate transporter in Saccharomyces cerevisiae

Molecular and Cellular Biology ◽

10.1128/mcb.12.7.2958-2966.1992 ◽

1992 ◽

Vol 12 (7) ◽

pp. 2958-2966

Author(s):

M Bun-Ya ◽

S Harashima ◽

Y Oshima

Keyword(s):

Saccharomyces Cerevisiae ◽

Amino Acid Residues ◽

Transport Activity ◽

Reading Frame ◽

Gtp Binding ◽

Pi Transport ◽

Recombination System ◽

Opposite Strand ◽

Constitutive Synthesis ◽

Site Specific Recombination System

We have found an open reading frame which is 1.1 kb upstream of PHO84 (which encodes a Pi transporter) and is transcribed from the opposite strand. In Saccharomyces cerevisiae, this gene is distal to the TUB3 locus on the left arm of chromosome XIII and is named GTR1. GTR1 encodes a protein consisting of 310 amino acid residues containing, in its N-terminal region, the characteristic tripartite consensus elements for binding GTP conserved in GTP-binding proteins, except for histidine in place of a widely conserved aspargine residue in element III. Disruption of the GTR1 gene resulted in slow growth at 30 degrees C and no growth at 15 degrees C; other phenotypes resembled those of pho84 mutants and included constitutive synthesis of repressible acid phosphatase, reduced Pi transport activity, and resistance to arsenate. The latter phenotypes were shown to be due to a defect in Pi uptake, and the Gtr1 protein was found to be functionally associated with the Pho84 Pi transporter. Recombination between chromosome V (at the URA3 locus) and chromosome XIII (in the GTR1-PHO84-TUB3 region) by using a plasmid-encoded site-specific recombination system indicated that the order of these genes was telomere-TUB3-PHO84-GTR1-CENXIII.

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Identification of a BALB/c-3T3 cell protein modulated by platelet-derived growth factor.

Molecular and Cellular Biology ◽

10.1128/mcb.3.1.70 ◽

1983 ◽

Vol 3 (1) ◽

pp. 70-81 ◽

Cited By ~ 34

Author(s):

C D Scher ◽

R L Dick ◽

A P Whipple ◽

K L Locatell

Keyword(s):

Growth Factor ◽

Dna Synthesis ◽

Cell Lines ◽

Actinomycin D ◽

Platelet Derived Growth Factor ◽

Cell Protein ◽

Transformed Cells ◽

Antigenic Determinants ◽

3T3 Cells ◽

Constitutive Synthesis

The platelet-derived growth factor (PDGF) stimulates density-arrested BALB/c-3T3 cells to synthesize a protein (pII; Mr, 35,000) that is constitutively synthesized by spontaneously transformed BALB/c-3T3 (ST2-3T3) cells which do not require PDGF for growth. Antisera against a major excreted protein family (MEP) of retrovirus-transformed cells quantitatively precipitated cellular pII. PDGF-stimulated pII has the same molecular weight, a similar charge, and similar antigenic determinants as authentic MEP isolated from ST2-3T3 or retrovirus-transformed cells. MEP represented about 2% of the nonnuclear proteins synthesized by ST2-3T3 cells and 0.3 to 0.6% of the proteins synthesized by PDGF-treated BALB/c-3T3 cells, a three- to sixfold increase over the background. In BALB/c-3T3 cells, less PDGF was required for pII (MEP) synthesis than for DNA synthesis. PDGF induced a selective increase in pII (MEP) within 40 min. Such preferential synthesis was inhibited by brief treatment with actinomycin D, suggesting a requirement for newly formed RNA. The constitutive synthesis of pII (MEP) by ST2-3T3 cells was not inhibited by actinomycin D. Five spontaneously or chemical carcinogen-transformed tumorigenic BALB/c-3T3 cell lines were studied; they neither required PDGF for growth nor responded to it. These cell lines became arrested at confluence with a G1 DNA content. Each of these independently isolated lines synthesized pII (MEP) constitutively. Thus, the synthesis of pII (MEP) may be required, but is not sufficient, for PDGF-modulated DNA synthesis.

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Significance of autogenously regulated and constitutive synthesis of regulatory proteins in repressible biosynthetic systems

Nature ◽

10.1038/258208a0 ◽

1975 ◽

Vol 258 (5532) ◽

pp. 208-214 ◽

Cited By ~ 29

Author(s):

Michael A. Savageau

Keyword(s):

Regulatory Proteins ◽

Constitutive Synthesis

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