The phospholipid composition of various strains of the yeast, Saccharomyces cerevisiae, and several of their derived mitochondrial mutants grown under conditions designed to induce variations in the complement of mitochondrial membranes has been examined . Wild type and petite (cytoplasmic respiratory deficient) yeasts were fractionated into various subcellular fractions, which were monitored by electron microscopy and analyzed for cytochrome oxidase (in wild type) and phospholipid composition . 90% or more of the phospholipid, cardiolipin was found in the mitochondrial membranes of wild type and petite yeast . Cardiolipin content differed markedly under various growth conditions . Stationary yeast grown in glucose had better developed mitochondria and more cardiolipin than repressed log phase yeast . Aerobic yeast contained more cardiolipin than anaerobic yeast . Respiration-deficient cytoplasmic mitochondrial mutants, both suppressive and neutral, contained less cardiolipin than corresponding wild types . A chromosomal mutant lacking respiratory function had normal cardiolipin content . Log phase cells grown in galactose and lactate, which do not readily repress the development of mitochondrial membranes, contained as much cardiolipin as stationary phase cells grown in glucose . Cytoplasmic mitochondrial mutants respond to changes in the glucose concentration of the growth medium by variations in their cardiolipin content in the same way as wild type yeast does under similar growth conditions. It is concluded that cardiolipin content of yeast is correlated with, and is a good indicator of, the state of development of mitochondrial membrane .

We have isolated cDNA clones from thyrotoxic (pMHCa) and normal (pMHC(8) adult rabbit hearts. Restriction map analysis and DNA sequence analyses show that, although there is strong homology between overlapping regions of the two clones, they are distinctly different. The two clones exhibited 78483% homology between the derived amino acid sequences and those determined by direct amino acid sequence analysis of rabbit fast skeletal muscle myosin heavy chains. The clones specify a segment of the myosin heavy chain corresponding to subfragment 2 and the COOH-terminal portions of subfragment 1. Nuclease S1 mapping was used to compare transcription of the two clones with expression of the a and (3 forms of myosin heavy chains in the ventricles of thyrotoxic, hypothyroid (propylthiouracil-treated), and normal rabbits. Thyrotoxic ventricles contained only pMHCa transcripts whereas hypothyroid ventricles contained exclusively pMHC(3 transcripts. These data correlate well with the presence of a-and (3-form myosin heavy chains. In the normal young adult rabbit, pMHC(3 transcripts predominate, agreeing with the known (3 form/a form ratio of 4: 1. We therefore conclude that pMHCa and pMHCP contain sequences of the a-and (-form myosin heavy chain genes, respectively.Myosin, a major contractile protein of skeletal and cardiac muscle, is composed of two 200,000-dalton heavy chains (HCs) and two sets oflow molecular weight light chains. The active center of myosin ATPase resides in the globular head of the heavy chain. This enzymatic activity is correlated with contractile velocity in skeletal muscle (1) and thus appears to be an important determinant of contractile function. Numerous polymorphic forms of myosin HC exist, not only in different types of muscle-e.g., fast and slow skeletal and cardiac-but also within each muscle type (2-12). Expression of these forms follows a developmental pattern (12-18) that may be altered by changes in the physiological (19-21) and hormonal (10-13) milieu ofthe cell.Cardiac ventricular muscle contains at least two formsreferred to as a and (3 (9)-of myosin HC. Electrophoresis of myosin under nondenaturing conditions reveals three bands; V1 and V3 are homodimers containing the a and 3 forms, respectively, whereas V2 is a heterodimer (9, 13). The ATPase activity of myosin with a-form HCs has been shown to be considerably higher than that of myosin with (-form .The expression of a-and (3form myosin HCs follows a defined developmental pattern that varies in different animal species. It has been shown that in rabbit the ( form/a form ratio is =3: 1 during the last halfofthe gestational period. After birth, the relative amount of the a form increases so that, during the first 2 wk postnatally, this ratio is 1: 1 (12, 14). Thereafter, the a form decreases and, in the old adult, the 3 form is present almost exclusively (12,14). In the young adult animals used in this study, the ( form/a form ratio was =4:1 (12 (27).Construction and Screening of cDNA Clones. Single-and double-stranded cDNA wa...

The expression of mRNAs for two cardiac myosins has been examined in the ventricles of hypo- and hyperthyroid rabbits by means of cloned cDNA sequences corresponding to the mRNAs of the alpha- and beta-myosin heavy chains (HCs). The temporal change in the relative levels of the alpha- and beta-HC mRNAs after 3,5,3'-triiodothyronine (T3) treatment of hypothyroid rabbits was determined by nuclease S1 mapping. In the hypothyroid state, only HC beta-mRNA was expressed in the ventricles. The HC alpha-mRNA was first detectable 4 h after administration of T3 (200 micrograms/kg) to hypothyroid animals. By 12 h, HC alpha-mRNA represented 20% of total myosin mRNA, increasing to 50% by 24 h and to about 90% by 72 h. The relationship between the relative mRNA levels and relative synthesis rates of the myosin HCs was evaluated in 5-6-week-old normal and thyrotoxic rabbits. Myosin synthesis rates were determined by labeling of protein in vivo with [3H]leucine. The V1 (HC alpha) and V3 (HC beta) isomyosins were separated by affinity chromatography with monoclonal antibodies, and the HCs were isolated electrophoretically. In a normal euthyroid group of animals and in animals 12 and 24 h after administration of 200 micrograms of 3,5,3',5'-tetraiodothyronine/kg, the relative mRNA levels and relative synthesis rates of the alpha- and beta-HCs were not significantly different. Our results show that, first, thyroid hormone causes a rapid accumulation of HC alpha-mRNA and loss of HC beta-mRNA and, second, in normal and thyrotoxic rabbits, the relative synthesis rates of HC alpha and HC beta reflect the relative abundance of the alpha- and beta-HC mRNAs.(ABSTRACT TRUNCATED AT 250 WORDS)