Cell-free protein synthesis in lysates of Drosophila melanogaster cells.

A procedure is described for preparing cell-free protein synthesizing lysates from Drosophila melanogaster tissue culture cells and embryos. Preparation of translationally active lysates from tissue culture cells is dependent on the presence of rat liver supernatant during cell lysis to inhibit ribonuclease activity. After micrococcal nuclease treatment of the lysate, protein synthesis is dependent on the addition of exogenous messenger RNA. The fidelity of translation is very high. The conditions for optimal translation have been determined. In addition, the effects on translation of a variety of supplements, including rat liver supernatant, have been analyzed. The products of translation by the Drosophila lysate have been compared with those of wheat germ extracts and of micrococcal nuclease treated rabbit reticulocyte lysates. Translation in vitro of bovine parathyroid hormone messenger RNA yielded two products tentatively identified as preproparathyroid hormone and proparathyroid hormone, as well as an unidentified third product. This result suggests that insect enzymes can accurately process mammalian precursor proteins.     

Drosophila choline acetyltransferase uses a non-AUG initiation codon and full length RNA is inefficiently translated

RNA from a partial cDNA clone containing the entire protein coding sequence of Drosophila melanogaster acetyl-CoA:choline O-acetyltransferase (EC 2.3.1.6; choline acetyltransferase) can be translated into active enzyme. This is unusual since this partial cDNA clone contains no appropriate ATG (AUG) initiation codon. In this study we use in vitro deletion and point mutants to identify GTG as the starting codon for protein translation. We also report the sequence of a full length Drosophila choline acetyltransferase cDNA and demonstrate that RNA produced by this clone is translated into active choline acetyltransferase but at a significantly reduced efficiency when compared to the partial cDNA clone. These results indicate that translational control may be an important regulatory step in production of Drosophila choline acetyltransferase.     

MES23.5细胞酪氨酸羟化酶的种属来源及其重组酶的活性测定

MES 2 3 5细胞作为研究神经变性疾病的工具 ,是一种杂交瘤性多巴胺能神经元细胞系 ,由大鼠胚胎中脑细胞与小鼠神经母细胞瘤 胶质瘤细胞系N18TG2杂交而成 .其酪氨酸羟化酶 (tyrosinehydroxylase ,TH)的动物种属来源不清楚 .应用反转录聚合酶链反应 (RT PCR)法从MES 2 3 5细胞系中克隆了编码TH的cDNA ;结构分析表明 ,其cDNA编码区由 14 97碱基构成 ,共编码 4 98个氨基酸 ,与大鼠和小鼠TH的同源程度分别为 93%和 10 0 % .该杂交瘤细胞系表达小鼠TH .将该cDNA亚克隆至原核表达载体pGEX 4T 1,经原核细胞表达、亲和层析得到了电泳纯的基因重组小鼠TH(recombinantmousetyrosinehydroxylase ,rmTH) .改良和建立了一种体外分析TH活性的新方法 .活性分析证明 ,纯化的rmTH能催化L 酪氨酸发生加单氧反应生成L 3,4 二羟基苯丙氨酸 (L 多巴 ) .rmTH的表观分子量为 5 6kD ;其酶促加单氧反应的最适pH值为 7 0 .乙二胺四乙酸能显著抑制此酶的活性 ,而亚铁离子能明显增强其活性 .     

Drosophila melanogaster has only one myosin alkali light-chain gene which encodes a protein with considerable amino acid sequence homology to chicken myosin alkali light chains.

A chimeric lambda DNA molecule containing the myosin alkali light-chain gene of Drosophila melanogaster was isolated. The encoded amino acid sequence was determined from the nucleic acid sequence of a cDNA homologous to the genomic clone. The identity of the encoded protein was established by two criteria: (i) sequence homology with the chicken alkali light-chain proteins and (ii) comparison of the two-dimensional gel electrophoretic pattern of the peptides synthesized by in vitro translation of hybrid-selected RNA to that of myosin alkali light-chain peptides extracted from Drosophila myofibrils. There is only one myosin alkali light-chain in D. melanogaster; its chromosomal location is region 98B . This gene is abundantly expressed during the development of larval as well as adult muscles. The Drosophila protein appears to contain one putative divalent cation-binding domain (an EF hand) as compared with the three EF hands present in chicken alkali light chains.     

Maternal and embryonic sources of tyrosine hydroxylase during Drosophila embryogenesis

Tyrosine hydroxylase (TH), the enzyme which catalyzes the conversion of tyrosine to L-DOPA and is rate limiting in catecholamine biosynthesis, is biochemically expressed in late stage wild-type Drosophila oocytes as well as in early embryogenesis. Null mutant alleles of TH (pale) are embryonic lethals with death occurring in the late embryonic or early larval periods of development. Staging of embryos demonstrated that inhibition of the enzymatic activity of TH by alpha-methyl-p-tyrosine (alphaMT) retards the progression of embryos primarily during the organogenesis stages of embryonic development, with lesser effects on earlier and later stages. On the other hand, time of gene action studies with a conditional temperature sensitive pale mutant (ple(ts1)) at its restrictive temperature (29 degrees C) indicate an onset of tyrosine hydroxylase gene action beginning in the oocyte stage of development. Thus, maternal as well as embryonic effects on the secretion and/or functionality of this enzyme may play roles in the early developmental program of the organism.     

The RNA-binding protein Staufen from rat brain interacts with protein phosphatase-1

In mammalian neurones, homologues of the Drosophila RNA-binding protein Staufen are part of ribonucleoprotein complexes that move bidirectionally along dendritic microtubules and appear to regulate mRNA translocation and translation. In this study, putative components of Staufen granules were identified in a yeast two-hybrid screen of a rat brain cDNA library with a rat Staufen bait. Protein phosphatase-1 was found as an interacting partner. Binding appears to be mediated by a five amino acid residue sequence motif (R-K-V-T-F) in Staufen that is conserved in a number of proteins interacting with the phosphatase. A two amino acid residue mutation within this motif (R-K-V-G-A) disrupted the interaction. A cytoplasmic interaction of both proteins was shown by coimmunoprecipitation of rat Staufen and protein phosphatase-1 from the cytoplasm of transfected cells and rat brain homogenates. In mammalian brain, the phosphatase represents the first described endogenous interaction partner of Staufen. In primary hippocampal neurones, both proteins partially colocalize in somata and neuronal processes. Staufen does not modulate the in vitro protein phosphatase activity. These findings show that protein phosphatase-1 is a native component of Staufen particles. Cellular functions of Staufen may be regulated via phosphorylation or Staufen may recruite the phosphatase into specific ribonucleoprotein complexes.     

Antibody to a human DNA repair protein allows for cloning of a Drosophila cDNA that encodes an apurinic endonuclease.

The cDNA of a Drosophila DNA repair gene, AP3, was cloned by screening an embryonic lambda gt11 expression library with an antibody that was originally prepared against a purified human apurinic-apyrimidinic (AP) endonuclease. The 1.2-kilobase (kb) AP3 cDNA mapped to a region on the third chromosome where a number of mutagen-sensitive alleles were located. The cDNA clone yielded an in vitro translation product of 35,000 daltons, in agreement with the predicted size of the translation product of the only open reading frame of AP3, and identical to the molecular size of an AP endonuclease activity recovered following sodium dodecyl sulfate-polyacrylamide gel electrophoresis of Drosophila extracts. The C-terminal portion of the predicted protein contained regions of presumptive DNA-binding domains, while the DNA sequence at the amino end of AP3 showed similarity to the Escherichia coli recA gene. AP3 is expressed as an abundant 1.3-kb mRNA that is detected throughout the life cycle of Drosophila melanogaster. Another 3.5-kb mRNA also hybridized to the AP3 cDNA, but this species was restricted to the early stages of development.     

Cloning and characterization of human and rat liver cDNAs coding for a gap junction protein

An extended synthetic oligonucleotide (58-mer) has been used to identify and characterize a human liver gap junction cDNA. The cDNA is 1,574 bases long and contains the entire coding region for a gap junction protein. In vitro translation of the RNA products of this cDNA is consistent with it coding for a 32,022-D protein. Southern blot analysis indicates that the gap junction gene is present as a single copy, and that it can be detected in a variety of organisms using the human liver cDNA as a probe. The human cDNA has been used to screen a rat liver cDNA library, and a rat liver junction cDNA clone has been isolated. The rat liver clone is 1,127 bases in length, and it has strong sequence homology to the human cDNA in the protein-coding region, but less extensive homology in the 3'-untranslated region.     

Isolation of a cloned DNA segment containing a ribosomal protein gene of Drosophila melanogaster

A Drosophila genomic DNA library in the vector Charon 4 was screened using cDNA derived from the small (6S-12S) poly(A)+ mRNA of 2-6-h-old Drosophila embryos. This fraction of mRNA is enriched for ribosomal protein-coding sequences. The selected recombinants were hybridized to total mRNA under conditions which allowed for isolation of homologous mRNAs. The mRNA from these RNA/DNA hybrids was eluted and translated in vitro. The translation products were analyzed by one- and two-dimensional electrophoresis with authentic ribosomal proteins as standards. One cloned DNA segment was found to contain a ribosomal protein gene, and a sequence which hybridizes strongly to at least 5 other ribosomal protein mRNAs.