Muscle RNA Research Articles

I/Lyn mouse phosphorylase kinase deficiency: mutation disrupts expression of the alpha/alpha'-subunit mRNAs.

A cDNA encoding the alpha subunit of mouse skeletal muscle phosphorylase kinase was used to compare the expression of alpha mRNAs in normal and phosphorylase kinase-deficient tissues of the I/Lyn mouse. The results demonstrate that two different molecular weight species of poly(A)+ RNA in normal mouse heart and skeletal muscle hybridize to the alpha cDNA. These two mRNAs direct the synthesis of alpha protein and its isoform alpha' in a cell-free translation system. Thus, alpha and alpha' are encoded by two distinct mRNAs. The abundance of both of these mRNAs is reduced dramatically in the phosphorylase kinase-deficient skeletal muscle and heart tissues from the I/Lyn mouse strain. This result indicates that a mechanism common to both alpha and alpha' expression is disrupted by the I/Lyn mutation. The I/Lyn deficiency is inherited as an X chromosome trait. By Southern mapping of Chinese hamster-mouse cell hybrids the alpha gene was localized to the mouse X chromosome, supporting the possibility that the I/Lyn mutation is in the alpha gene. These results are discussed in terms of a cis or trans mutation influencing the expression of either a single alpha/alpha' gene or two genes encoding alpha and alpha'.

Altered growth and protein turnover in rats fed sodium-deficient diets.

The effects of feeding a sodium-deficient (NaD) diet were examined in young, growing rats. All animals were fed the same diet and drank distilled water. In the control group the water contained 37 mM sodium chloride. After 2-3 wk body composition measurements were performed and epitrochlearis muscle protein synthesis and degradation rates determined. The experimental group gained only 45% of the wt and 70% of the length seen in the control group. The difference in wt gain could not be accounted for by differences in extracellular volume which averaged only 4% of body wt. Although total food intake was equivalent in both groups, urinary ammonia plus urea nitrogen excretion was higher in the experimental animals. Protein synthesis, measured as the incorporation of 14C-phenylalanine into muscle protein was significantly lower in NaD rats (56.58 versus 68.79) and (65.26 versus 83.88 nmol phenylalanine/h/g wet wt (both p less than 0.01) when incubated with or without the addition of insulin (1 mU/mL). Net protein degradation rates were unchanged. Gastrocnemius muscle RNA concentrations were also lower in NaD rats (1.09 versus 1.52 mg/g wet wt, p less than 0.001). There were no changes noted in the concentration of protein within either gastrocnemius or epitrochlearis muscles. These results suggest that in rats, the growth failure seen in sodium deficiency: 1) affects both length and wt gain; 2) is not associated with decreased nutrient intake; 3) is due to decreased rates of muscle protein synthesis without affecting net protein degradation rates; and 4) is associated with diminished muscle tissue RNA concentrations.

Notes: Effects of Tissue Collection and Storage Methods on Nucleic Acid Determinations in White Muscle of Fishes

We determined the concentrations of RNA and DNA in white muscle of rainbow trout Oncorhynchus mykiss and fathead minnow Pimephales promelas that had been frozen in either liquid nitrogen, a lowtemperature freezer (–80°C), or a household freezer (–20°C), or had been left 1–24 h after death in either wet ice or cold water (8.5–9.5°C). Both RNA and DNA were resistant to enzymatic breakdown because their concentrations and the RNA:DNA ratio did not differ significantly among treatments in either species. However, there was a tendency for muscle DNA concentration to decrease in fathead minnow stored in water for 24 h. Paired samples of rainbow trout muscle, both of which were frozen in liquid nitrogen but one of which was thawed and refrozen before analysis, differed significantly in DNA concentration and RNA:DNA ratio. The refrozen samples had significantly lower DNA concentrations, which led to significantly higher RNA: DNA ratios.

Primary structure of rabbit skeletal muscle glycogen synthase deduced from cDNA clones

The complete amino acid sequence of rabbit skeletal muscle glycogen synthase was deduced from cDNA clones with a composite length of 3317 bp. An mRNA of 3.6 kb was identified by Northern blot analysis of rabbit skeletal muscle RNA. The mRNA coded for a protein of 734 residues with a molecular weight of 83,480. The deduced NH2-terminal and COOH-terminal sequences corresponded to those reported for the purified protein, indicating the absence of any proteolytic processing. At the nucleotide level, the 5' untranslated and coding regions were 79 and 90% identical for rabbit and human muscle glycogen synthases, whereas the 3' untranslated regions were significantly less similar. The enzymes had 97% amino acid sequence identity. Interestingly, the NH2 and COOH termini of rabbit and human muscle glycogen synthase, the regions of phosphorylation, showed the greatest sequence variation (15 of 19 mismatches and two insertion/deletion events), which may indicate different evolutionary constraints in the regulatory and catalytic regions of the molecule.

Tissue-specific expression of four types of rat calmodulin-dependent protein kinase II mRNAs

cDNA clones for a fifth polypeptide of rat brain calmodulin-dependent protein kinase II were isolated and sequenced. The cDNA sequence encoded a polypeptide, designated delta, consisting of 533 amino acid residues with a molecular weight of 60,080. Comparison of amino acid sequences of this and alpha, beta, beta', and gamma polypeptides of calmodulin-dependent protein kinase II reveals marked homology among them. The mRNAs for delta were expressed in rat brain tissues with different regional specificities. The distribution of alpha, beta/beta', gamma, and delta mRNAs in cerebrum, skeletal muscle, diaphragm, heart, small intestine, uterus, aorta, liver, kidney, lung, and testis were examined by RNA blot hybridization analysis with probes specific for the respective mRNAs. A 3.9-kilobase (kb) RNA species hybridizable with a probe for gamma was found in all the tissues examined, and 4.0-4.2-kb RNA species hybridizable with a probe for delta were found in all the tissues examined except for liver, while a 4.8-kb RNA species hybridizable with a probe for alpha and a 4.2-kb RNA species hybridizable with a probe for beta were present in brain but not in the other tissues. With the alpha probe, however, a 4.1- and 2.6-kb RNA species were both detected in skeletal muscle and diaphragm. With the beta probe, a 4.3-kb RNA in skeletal muscle and diaphragm, 2.9-kb RNA in small intestine, and 4.0-kb RNA in testis were detected. With the delta probe, a 3.5-kb RNA in heart and 1.8-kb RNA in testis were detected. Thus, gamma and delta mRNAs were expressed in various tissues, while alpha and beta/beta' mRNAs were primarily, if not exclusively, expressed in brain.

Muscle Protein Metabolism in Finishing Pigs Fed Ractopamine

Forty crossbred barrows (average initial weight, 66.4 kg) were utilized to determine the effects of ractopamine (a phenethanolamine/beta adrenergic agonist) on protein accretion and synthesis, activities of cathepsins B, H, L and calcium-dependent proteinase and nucleic acid content of semitendinosus muscle (ST). All pigs were offered a 16% protein, mineral and vitamin fortified corn-soybean meal diet supplemented with either 0 or 20 ppm ractopamine for 14, 21, 28, 35 or 42 d. Protein synthesis (fractional rates) was studied in pigs at d 21 and 35; ST protease activities, protein and nucleic acid content were measured on d 14, 28 and 42. Ractopamine increased (P less than .01) ST total protein content and maintained RNA muscle concentration and total ST muscle RNA content. DNA content (mg/g ST) declined (P less than .05) upon ractopamine feeding, but total DNA per muscle remained unchanged except for d 42, when the ST muscles were largest. Fractional accretion rates (FAR) were 1.0 and 1.2% for control and ractopamine-fed pigs, respectively. Fractional protein synthesis rate (FSR) was higher (P less than .06) in ractopamine-fed pigs (6.1%/d) than in control pigs (4.4%/d). Fractional protein synthesis rate could account for the observed muscle hypertrophy and increased FAR. Estimated fractional breakdown rates (FBR = FSR - FAR) were 3.4%/d and 4.9%/d for control and ractopamine-fed pigs, respectively. The activities of the catheptic proteases and calcium-dependent proteinase were not affected by the treatments.

Identification of the Functional Promoter Regions in the Human Gene Encoding the Myosin Alkali Light Chains MLC1 and MLC3 of Fast Skeletal Muscle

The human gene encoding the alkali myosin light chains (MLC) 1 and 3 of fast skeletal muscle has been isolated. Two separate start sites for transcription have been identified by S1 analysis of muscle RNA. The nucleotide sequences of both proximal promoter regions have been determined and compared to the corresponding gene regions of other species. Several conserved promoter elements were located within 140 nucleotides upstream of the mRNA cap site, whereas further upstream no homologous sequences were found. Unidirectional 5' deletion mutants of both MLC promoters were used to direct bacterial chloramphenicol acetyltransferase activity in transient transfection assays of muscle and nonmuscle cells. Approximately 120 nucleotides of the MLC1 promoter and 80 nucleotides of the MLC3 promoter were sufficient for the transcriptional activation in primary myotubes and to a lower degree also in fibroblasts and hepatocytes. The preferential expression in muscle cells was not dependent on the conserved MLC consensus sequence, CCTTTTATAG, but it absolutely required the CCAT box or the CAT-like box in the MLC1 and MLC3 promoters, respectively. The weak activity of the MLC1 promoter was markedly enhanced in myotubes when DNA from the 3' gene flanking sequence was included in the chloramphenicol acetyltransferase constructs.

USE OF THE LIEBER—DECARLILIQUID FEEDING REGIME WITH SPECIFIC REFERENCE TO THE EFFECTS OF ETHANOL ON RAT SKELETAL MUSCLE RNA

This communication discusses the ways in which parameters of tissue injury in chronic ethanol-fed rats can be presented. These are: concentration (amount per unit wet weight), absolute amount (total quantity per organ or tissue) or relative to body weight (total quantity per unit body weight). Specific reference is made to the amount of RNA in skeletal muscles from rats fed the Lieber-DeCarli liquid diet containing ethanol for 6 weeks. Comparisons were made with data from rats which were pair-fed the same diet in which ethanol was substituted by iso-caloric glucose. Chronic ethanol-feeding had no statistically significant effect on the concentration of skeletal muscle RNA, though the absolute amount was reduced by 20%. When expressed relative to body weight the magnitude of this decline was reduced, to only 10%. Due to the nature of the liquid feeding regime the animals showed variable alterations in body weight. The amount of liquid diet consumed by control and ethanol-fed rats over a 24 hr period can comprise as much as 40% (w/w) of body weight. It is therefore suggested that data expressed relative to body mass may, on occasions, be erroneous. Episodic engorgement with food may also have an influence on other metabolic processes such as the kinetics of protein, fat or carbohydrate metabolism. These issues may have important implications for other studies using the Lieber-DeCarli liquid diet to examine the effects of ethanol on muscle or non-muscle tissues.

Muscle cell potassium, RNA and hydration in pregnancy and pre-eclampsia

Thirty four pregnant women from 26 to 38 weeks gestation and 24 pregnant women with pre-eclampsia gave samples of muscle (rectus abdominis) at caesarean section. Muscle samples were analysed for H 2O, K +, Mg 2+ and Na +. Cell extracellular H 2O was partitioned by the use of the Cl - space. Also protein, nucleic acids and Zn 2+ were determined. From 26 to 38 weeks gestation the concentration of K + per litre of cell water ([K i ]) slowly declined. The slope was significant. Points for patients with pre-eclampsia fell below the line and analysis of covariance showed that the two populations were different ( P < 0.001). Patients A—J were regarded clinically as severe pre-eclamptics. Points for these patients, in general, fell between 1 and 2 SDs below the normal line. Since other cations per litre of muscle cell water did not change, questions are raised. Is the cation gap filled by amino acids or does vascular spasm cause a leakage of K + from muscle cells? Does hypotonicity eventually develop leading to water intoxication? The low oncotic pressure in pre-eclampsia (shown here), the negative free water clearance could all favour increased cell hydration (some evidence for this is presented here towards term). Assessment of available information concerning creatinine excretion during normal pregnancy and K 40, K 42 studies together with our own rodent studies leads us to believe that a significant increase in muscle mass occurs, but such may not be the case in pre-eclampsia since the reduction in RNA and Zn 2+ concentrations in muscle would suggest excessive protein degradation. Our understanding of changes in body composition in pregnancy is incomplete –even more so in pre-eclampsia.

Expression of myosin heavy chain transcripts during Xenopus laevis development

In amphibians, the composition and pattern of expression of the myosin heavy chain (myHC) gene family are mostly unknown. To understand better the regulation of this complex family, we screened cDNA libraries from swimming tadpole and adult leg muscle RNA and have isolated and partially sequenced clones for several myHCs. Two of these, E3 and E19, first appear in mesoderm at late gastrula stage and are coexpressed with muscle actin. They increase in abundance in trunk and tail myotome until metamorphosis, when they begin to decline. E3 and E19 are also both expressed in hind leg muscle at the beginning of metamorphosis, but decline to low levels in adult leg muscle. A new transcript, A7, first appears during early metamorphosis in both the tail and hind leg skeletal muscle. A7 transcripts then decline in degenerating tail but persist in hind leg through metamorphosis and in adults. Two other embryonic myHCs, E14 and E15, code for isoforms closely related to E19 and may be alleles or duplications. Although sequence comparisons with myHCs from other vertebrates could not correlate the transcripts with specific protein isoforms, from the pattern of expression E3 and E19 apparently code for embryonic fast skeletal myHC isoforms, whereas A7 codes for an adult skeletal isoform.

Expression of avian Ca2+-ATPase in cultured mouse myogenic cells.

cDNA encoding Ca2+-ATPase was cloned from a chicken skeletal muscle library. The cDNA (termed FCa) comprised 3,239 base pairs, including an open reading frame encoding 994 amino acids which showed the highest degree of homology with the adult rabbit fast-twitch Ca2+-ATPase isoform (C. J. Brandl, S. de Leon, D. R. Martin, and D. H. MacLennan, J. Biol. Chem. 262:3768-3774, 1987). Radiolabeled FCa hybridized to a 3.2-kilobase transcript in chicken skeletal muscle RNA but not to cardiac muscle RNA, which confirmed its identity as encoding the fast Ca2+-ATPase isoenzyme. FCa was transfected into the mouse myogenic line C2C12, from which a protein of 100 kilodaltons was immunopurified by using a monoclonal antibody specific for the avian fast Ca2+-ATPase. Immunofluorescence microscopy of a line (designated C2FCa2) stably expressing the avian Ca2+-ATPase localized the protein to the nuclear envelope and a population of cytoplasmic vesicles. A similar pattern was observed when C2FCa2 cells were stained with DiOC6(3), a cyanine dye that labels endoplasmic reticulum and mitochondria (M. Terasaki, J. Song, J. R. Wong, M. J. Weiss, and L. B. Chen, Cell 38:101-108, 1984). We conclude that the avian Ca2+-ATPase fast isoform is expressed and correctly targeted to the endoplasmic reticulum in mouse C2C12 cells.

Expression of Avian Ca2+-ATPase in Cultured Mouse Myogenic Cells

cDNA encoding Ca2+-ATPase was cloned from a chicken skeletal muscle library. The cDNA (termed FCa) comprised 3,239 base pairs, including an open reading frame encoding 994 amino acids which showed the highest degree of homology with the adult rabbit fast-twitch Ca2+-ATPase isoform (C. J. Brandl, S. de Leon, D. R. Martin, and D. H. MacLennan, J. Biol. Chem. 262:3768-3774, 1987). Radiolabeled FCa hybridized to a 3.2-kilobase transcript in chicken skeletal muscle RNA but not to cardiac muscle RNA, which confirmed its identity as encoding the fast Ca2+-ATPase isoenzyme. FCa was transfected into the mouse myogenic line C2C12, from which a protein of 100 kilodaltons was immunopurified by using a monoclonal antibody specific for the avian fast Ca2+-ATPase. Immunofluorescence microscopy of a line (designated C2FCa2) stably expressing the avian Ca2+-ATPase localized the protein to the nuclear envelope and a population of cytoplasmic vesicles. A similar pattern was observed when C2FCa2 cells were stained with DiOC6(3), a cyanine dye that labels endoplasmic reticulum and mitochondria (M. Terasaki, J. Song, J. R. Wong, M. J. Weiss, and L. B. Chen, Cell 38:101-108, 1984). We conclude that the avian Ca2+-ATPase fast isoform is expressed and correctly targeted to the endoplasmic reticulum in mouse C2C12 cells.

Effect of chronic ethanol ingestion on tissue RNA and blood flow in skeletal muscle with comparative reference to bone and tissues of the gastrointestinal tract of the rat

1. The effects of feeding a diet containing ethanol as 36% of total calories for 4-5 weeks on muscle RNA content and blood flow was investigated in male rats weighing 150-250 g. Control animals were pair-fed the same diet in which ethanol was substituted by isocaloric glucose. 2. Chronic ethanol consumption reduced the capacity for type II (anaerobic, fast-twitch) fibre-rich skeletal muscles to synthesize protein as reflected by a decreased RNA/protein ratio. Type I (aerobic, slow-twitch) fibre-rich muscles were unaffected. 3. Ethanol feeding had no significant effect on cardiac output. Furthermore, the percentage of cardiac output to type I and type II fibre-rich muscles, bone and tissues of the gastrointestinal tract, i.e. stomach, small intestine and large intestine, was unaffected by ethanol consumption. Similarly, ethanol feeding had no effect on blood flow when it was calculated on the basis of tissue weight (ml min-1 g-1). 4. It was concluded that chronic ethanol feeding in the rat was associated with selective skeletal muscle dysfunction in the absence of changes in blood supply.

Transcriptional regulation of decreased protein synthesis during skeletal muscle unloading.

Muscle atrophy resulting from disuse is associated with marked decrements in protein synthesis. The objective of the present investigation was to determine levels of total muscle RNA and the content and composition of the mRNA fraction as a qualitative assessment of the potential regulatory role of transcriptional alterations in unloaded skeletal muscles. Hindlimb muscle unloading was produced by whole-body suspension of rats for up to 7 days. The soleus, gastrocnemius, and extensor digitorum longus (EDL) were excised from 1-, 3-, and 7-day suspended and pair-fed controls, and RNA was extracted by homogenization in 5 M guanidinium thiocyanate. Total RNA and mRNA contents were lower in soleus and gastrocnemius after 7 days of suspension compared with pair-fed controls, but total RNA and mRNA concentrations (per g muscle and per microgram total RNA, respectively) were unaltered. alpha-Actin mRNA, assessed by dot blot hybridization, was significantly reduced in soleus after 1 (37%), 3 (28%), and 7 (59%) days of suspension and in gastrocnemius after 3 (44%) and 7 (41%) days. However, alpha-actin mRNA was unchanged in the EDL after suspension. Protein synthesis directed by RNA extracted from soleus and EDL indicated marked (30-400%) alterations in mRNAs coding for several small (15- to 25-kDa) proteins. The results of this study suggest that altered transcription and availability of specific mRNAs could contribute significantly to the regulation of protein synthesis during unloading of skeletal muscle.

Identification of a novel nicotinic acetylcholine receptor structural subunit expressed in goldfish retina.

A new non-alpha (n alpha) member of the nicotinic acetylcholine receptor (nAChR) gene family designated GFn alpha-2 has been identified in goldfish retina by cDNA cloning. This cDNA clone encodes a protein with structural features common to all nAChR subunits sequenced to date; however, unlike all known alpha-subunits of the receptor, it lacks the cysteine residues believed to be involved in acetylcholine binding. Northern blot analysis shows multiple transcripts hybridizing to the GFn alpha-2 cDNA in goldfish retina but undetectable levels of hybridizable RNA in brain, muscle, or liver. S1 nuclease protection experiments indicate that multiple mRNAs are expressed in retina with regions identical or very similar to the GFn alpha-2 sequence. In situ hybridization shows that the gene encoding GFn alpha-2 is expressed predominantly in the ganglion cell layer of the retina.

Molecular characterization of rat skeletal muscle myosin light chain kinase

A 1.85-kilobase (kb) cDNA has been isolated that encodes the catalytic and calmodulin binding domains of rat skeletal muscle myosin light chain kinase. The cDNA hybridized to a 3.3-kb RNA present in fast- and slow-twitch skeletal muscles. The reported enzymatic activity (3-fold greater in fast- than slow-twitch skeletal muscles) reflects the relative abundance of this RNA in the two types of skeletal muscle. No hybridization of the cDNA was detected to RNA isolated from smooth or nonmuscle tissues. The clone cross hybridized to a 2.2-kb RNA present in cardiac tissue. Ribonuclease protection analysis of skeletal and cardiac muscle RNA revealed major differences in the two hybridizing RNAs. Thus rat skeletal muscle contains a single myosin light chain kinase isoform, which is distinct from the cardiac, smooth, and nonmuscle forms.

McArdle's disease: biochemical and molecular genetic studies.

We have analyzed muscle biopsy specimens from 48 patients with biochemically proven phosphorylase deficiency (McArdle's disease) by sodium dodecylsulphate polyacrylamide gel electrophoresis (SDS-PAGE), immunoblotting, and immunotitration (enzyme-linked immunosorbent assay [ELISA]). Thirty-five of the 42 patients studied by SDS-PAGE and immunoblot, and 41 of the 48 patients studied by ELISA had no detectable enzyme protein. Six patients had markedly decreased phosphorylase protein by all three assays, and only 1 patient had a normal amount of protein. No apparent correlation existed between the presence or absence of enzyme protein and the clinical presentation or muscle glycogen concentration. Northern analysis was performed on muscle RNA in 4 patients: messenger RNA was normal in 2, abnormally short in 1, and absent in the fourth, indicating heterogeneity of the molecular lesion in McArdle's disease.

Effects of Dietary Protein and Energy Levels on Weight Gains, Body Composition, and RNA: DNA Ratios of Fingerling Walleyes

Abstract The effects of various levels of dietary energy and protein on the growth rate, body composition, and muscle RNA:DNA ratios of walleyes (Stizostedion vitreum) were studied during a 10-week period. A factorial treatment design was used to provide three levels of dietary metabolizable energy (ME), 3,310, 3,530, and 3,750 kcal ME/kg diet, and four levels of protein, 37, 44, 51, and 58%. Both dietary protein and energy affected weight gain and length change (P < 0.05), but no interaction effects were observed. Maximum weight gain occurred with the 51% protein and 3,530 kcal ME!kg diet. Neither dietary protein nor energy affected the condition factor of the fish. The percentages of body fat, protein, ash, and moisture were affected by dietary protein (P < 0.05), but only body fat and moisture were affected by dietary energy (P < 0.05). The percentage of body fat decreased as dietary protein was increased, but it increased as dietary energy was increased. The percentage of body moisture varied inversel...

The effect of chronic ethanol ingestion on protein metabolism in type-I- and type-II-fibre-rich skeletal muscles of the rat

1. The effects of chronic ethanol feeding on muscles containing a predominance of either Type I (aerobic, slow-twitch) or Type II (anaerobic, fast-twitch) fibres were studied. Male Wistar rats, weighing approx. 90 g or 280 g, were pair-fed on a nutritionally complete liquid diet containing 36% of total energy as ethanol, or isovolumetric amounts of the same diet in which ethanol was replaced by isoenergetic glucose. After 6 weeks feeding, fractional rates of protein synthesis were measured with a flooding dose of L-[4-(3)H]-phenylalanine and muscles were analysed for protein, RNA and DNA. 2. Ethanol feeding decreased muscle weight, protein, RNA and DNA contents in both small and large rats. Type-II-fibre-rich muscles showed greater changes than did Type-I-fibre-rich muscles. Changes in protein paralleled decreases in DNA. 3. The capacity for protein synthesis (RNA/protein), fractional rates of protein synthesis and absolute rates of protein synthesis were decreased by ethanol feeding in both small and large rats. The amounts of protein synthesized relative to RNA and DNA were also decreased. Changes were less marked in Type-I than in Type-II-fibre-rich muscles. Loss of protein, RNA and DNA was greater in small rats, but protein synthesis was more markedly affected in large rats. 4. It was concluded that chronic ethanol feeding adversely affects protein metabolism in skeletal muscle. Fibre composition and animal size are also important factors in determining the pattern of response.

Response of skeletal muscle RNA polymerases I and II to tumour growth

The muscle wasting which occurs in animals bearing a transplantable tumour is accompanied by a decrease in the level of protein synthesis and a loss in RNA. This paper examines the behaviour of RNA polymerases I and II (EC 2.7.7.6) in nuclei isolated from skeletal muscle of rats bearing a Walker 256 carcinoma. Marked decreases were observed in template-engaged RNA polymerase I and II activities and in free RNA polymerase I activity. Free RNA polymerase II activity was unaltered. When assays were carried out at high (NH 4) 2SO 4 concentration or in the presence of heparin the diminished RNA polymerase I activity was still apparent, but heparin and high ionic strength overcame the inhibition of RNA polymerase II. Loss of RNA polymerase I activity was associated with a decrease in the number of template-engaged enzyme molecules and in the polynucleotide elongation rate. The number of template-engaged RNA polymerase II molecules was unaltered by tumour growth, but the polynucleotide elongation rate was significantly reduced. No evidence was obtained for any alteration in ribonuclease activity in nuclei or whole muscles of tumour-bearing rats. These results demonstrate an effect of the tumor on transcription in skeletal muscle of its host.