Temperature-sensitive Escherichia coli mutant with an altered initiation codon of the uncG gene for the H+-ATPase gamma subunit

Correlation of mitochondrial protein expression in complexes I to V with natural and induced forms of canine idiopathic dilated cardiomyopathy

OBJECTIVE

To identify qualitative and quantitative differences in cardiac mitochondrial protein expression in complexes I to V between healthy dogs and dogs with natural or induced dilated cardiomyopathy (DCM).

SAMPLE POPULATION

Left ventricle samples were obtained from 7 healthy dogs, 7 Doberman Pinschers with naturally occurring DCM, and 7 dogs with DCM induced by rapid right ventricular pacing.

PROCEDURES

Fresh and frozen mitochondrial fractions were isolated from the left ventricular free wall and analyzed by 2-dimensional electrophoresis. Protein spots that increased or decreased in density by 2-fold or greater between groups were analyzed by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry or quadrupole selecting, quadrupole collision cell, time-of-flight mass spectrometry.

RESULTS

A total of 22 altered mitochondrial proteins were identified in complexes I to V. Ten and 12 were found in complex I and complexes II to V, respectively. Five were mitochondrial encoded, and 17 were nuclear encoded. Most altered mitochondrial proteins in tissue specimens from dogs with naturally occurring DCM were associated with complexes I and V, whereas in tissue specimens from dogs subjected to rapid ventricular pacing, complexes I and IV were more affected. In the experimentally induced form of DCM, only nuclear-encoded subunits were changed in complex I. In both disease groups, the 22-kd subunit was downregulated.

CONCLUSIONS AND CLINICAL RELEVANCE

Natural and induced forms of DCM resulted in altered mitochondrial protein expression in complexes I to V. However, subcellular differences between the experimental and naturally occurring forms of DCM may exist.

Synthase (H(+) ATPase): coupling between catalysis, mechanical work, and proton translocation

Coupling with electrochemical proton gradient, ATP synthase (F(0)F(1)) synthesizes ATP from ADP and phosphate. Mutational studies on high-resolution structure have been useful in understanding this complicated membrane enzyme. We discuss mainly the mechanism of catalysis in the beta subunit of F(1) sector and roles of the gamma subunit in energy coupling. The gamma-subunit rotation during catalysis is also discussed.

Effects of deletions in the uncA-uncG intergenic regions on expression of uncG, the gene for the gamma subunit of the Escherichia coli F1Fo-ATPase

The gamma subunit of the E. coli F1Fo-ATPase is coded for by uncG. This gene is poorly expressed compared to uncA (alpha subunit), which precedes uncG in the unc operon. The genes are separated by a 50-nucleotide intergenic region. We examined the effects of a set of deletions in this region on the relative expression of uncA'-'lacZ and uncG'-'lacZ translational fusion genes located either in the chromosomal unc operon or at the chromosomal lambda att site. The gene for the alpha subunit was expressed 3-6-times better than the gene for the gamma subunit, depending upon chromosomal location. Deletion analysis revealed that the uncA-uncG intergenic region significantly affects expression of uncG, but the Shine-Dalgarno region is not absolutely required for expression of uncG. Different deletions resulted in either increased or decreased expression of uncG.

Translational coupling in a penP-lacZ gene fusion in Bacillus subtilis and Escherichia coli: use of AUA as a restart codon

An out-of-frame fusion between the penicillinase gene (penP) of Bacillus licheniformis and the beta-galactosidase gene (lacZ) of Escherichia coli was shown to direct the synthesis of an active beta-galactosidase with the same electrophoretic mobility as the wild-type protein, both in B. subtilis and E. coli. This synthesis was dependent on translation of the truncated penP gene and appeared to result from translational coupling. The fusion point between penP and lacZ contained the sequence AUAG, in which the UAG and AUA codons were in-frame with the penP and lacZ reading units, respectively. N-terminal amino acid sequence analysis of the beta-galactosidase protein suggested that, both in B. subtilis and E. coli, reinitiation of translation occurred at the AUA codon present at the gene fusion point.