No abstract

The complete nucleotide sequence of the mitochondrial DNA (mtDNA) molecule of the parasitic nematode worm Ascaris suum has been determined. This molecule lacks genes for tRNAs of the standard form. Instead, 21 sequences are found that can be folded into structures that resemble tRNAs in which the TIC arm and variable loop are missing and replaced with a single loop of between 4 and 12 nucleotides. Considerations of various properties of these sequences, including the number, predicted anticodons, conserved nucleotides, direction of transcription, base composition, and relative gene arrangements are consistent with the interpretation that they are genes for a different sort of tRNA. Transfer RNA genes with a similar potential secondary structure are found in mtDNA of the free-living nematode Caenorhabditis elegans, suggesting that this unusual form of tRNA is used by all nematode mitochondria.

Studies were conducted to determine relationships between feed efficiency and mitochondrial function and biochemistry. After feed efficiency (FE; gain:feed) was determined in broiler breeder males between 6 and 7 wk of age, mitochondria were isolated from breast and leg muscle from birds with high FE (0.83+/-0.01, n = 6) and low FE (0.64+/-0.01, n = 7). Respiratory chain coupling, assessed by the respiratory control ratio (RCR), was greater in high FE breast, and leg mitochondria provided NADH-linked, but not FADH-linked, energy substrates. There were no differences, however, in the adenosine diphosphate to oxygen (ADP:O) ratio (an index of oxidative phosphorylation) when mitochondria were provided either energy substrate. Electron leak, as determined by generation of H202, was greater in the low FE than in high FE breast mitochondria. Electron leak increased following inhibition of electron transport at Complex I (with rotenone) and Complex III (with antimycin A) in low FE but not in high FE breast mitochondria. There were no differences in basal electron leak in leg mitochondria between groups, but H202 generation was elevated (P < 0.07) compared to basal values in low FE leg mitochondria after Complex I inhibition. The activities of Complexes I and II were greater in high FE breast and leg muscle mitochondria compared to those in low FE mitochondria. The results indicate that lower respiratory chain coupling in low FE muscle mitochondria may be due to lower activities of Complexes I and II and defects in electron leak and provide insight into cellular mechanisms associated with the phenotypic expression of feed efficiency in broilers.

, did not show any specific binding to the radioligand, but were found to be constitutively active in the cAMP assay. The E and E R alleles are associated with black feather colour in chicken while the e b allele gives rise to brownish pigmentation. The three constitutively active receptors share a mutation of Glu to Lys in position 92. This mutation was previously found in darkly pigmented sombre mice, but constitutively active MC receptors have not previously been shown in any nonmammalian species. We also inserted the Glu to Lys mutation in the human MC1 and MC4 receptors. In contrast with the chicken clones, the hMC1-E94K receptor bound to the ligand, but was still constitutively active independently of ligand concentration. The hMC4-E100K receptor did not bind to the MSH ligand and was not constitutively active. The results indicate that the structural requirements that allow the receptor to adapt an active conformation without binding to a ligand, as a consequence of this E/K mutation, are not conserved within the MC receptors. The results are discussed in relationship to feather colour in chicken, molecular receptor structures and evolution. We suggest that properties for the ÔE92K switchÕ mechanism may have evolved in an ancestor common to chicken and mammals and were maintained over long time periods through evolutionary pressure, probably on closely linked structural features.Keywords: G-protein coupled; MSH; melanocortin receptor; polymorphism.Spontaneous or constitutive G-protein coupled receptor (GPCR) activity was first convincingly described for the d-opioid receptor [1], and was further established by the demonstration of constitutive activity in chimeras of the a 1B and a 2 receptors (summarized in [2]). Later it was shown that mutations in the human rhodopsin gene can constitutively activate transducin in the absence of retinal and light [3]. It is now known that naturally occurring constitutively active GPCRs are found to be responsible for a diverse array of inherited as well as somatic genetic disorders [4,5].The melanocortins (a-MSH/ACTH), secreted from a frog pituitary, were in 1912 found to cause pigmentation.In higher vertebrates including aves and mammals, these peptides are expressed throughout the body, and are involved in a variety of physiological regulatory functions [6][7][8]. In the skin, the melanocortins are synthesized locally (for birds [9], for mammals [10]), and act through a GPCR named melanocortin (MC) 1 receptor to regulate melanogenesis. Keratinocytes probably serve as the main physiological source of melanocortins acting on melanocytes in the epidermis and hair follicle. The MC1 receptor couples through G proteins to adenylate cyclase to stimulate tyrosinase, the rate-limiting enzyme in the synthesis of both classes of melanin pigments, eumelanin and phaeomelanin. A low level of tyrosinase expression leads to increased phaeomelanin synthesis, while elevated levels of tyrosinase, that can result from a-MSH stimulation of melanocytes, divert the intermediates primarily a...

The mitochondrial DNA (mtDNA) molecules of the nematode worms, Caenorhabditis elegans and Ascaris suum contain 22 putative genes for non‐standard forms of tRNAs. The inferred transcripts can be folded into 20 separate structures each resembling a tRNA whose T psi C arm and variable loop are replaced with a simple loop of 6‐12 nucleotides. In two further structures [that resemble tRNAs for ser(UCN) and ser(AGN)], the dihydrouridine arm is replaced by a loop of 5‐8 nucleotides. By hybridizing mt‐tRNA gene‐specific oligonucleotide probes to nematode RNAs, we have obtained evidence for transcription of at least nine C.elegans and three A.suum mt‐tRNA genes. Each transcript (tRNA) is the exact size predicted from the respective DNA sequence, to which three nucleotides, presumably CCA, have been added following transcription. An exception was C.elegans mt‐tRNAasn, most molecules of which had one nucleotide (plus CCA) more than predicted from the gene. The data presented strongly support the conclusion that the functional mt‐tRNAs of nematode worms are direct transcripts (with only CCA addition) of the structurally unusual mt‐tRNA genes. There is no evidence of trans‐splicing or RNA editing to add the sequences missing from these nonstandard tRNAs. We presume, therefore, that the non‐standard forms are active in mitochondrial protein synthesis.