The artificial AT-rich block enhanced the production of bovine growth hormone in Escherichia coli

In order to increase the synthesis of bovine growth hormone (bGH) using T7 promoter system in E. coli, the artificial AT-rich block was introduced into the upstream region of a consensus Shine-Dalgarno (SD) sequence and the spacer region (between SD and ATG codon) was enriched with A and T nucleotides. The cells harboring pTAJ plasmids with AT-rich block produced bGH in the range of 3% to 25% and the cells harboring pTBJ plasmids with AT-rich sequence in the spacer region from 0.8% to 20% of total cell proteins. This result suggests that AT rich block and AT nucleotides in the spacer region destabilize mRNA secondary structure, depending on the downstream coding information of bGH gene and also, implying that the disruption of mRNA secondary structure might be a major factor for regulating bGH expression in the translational initiation process.     

Enhancement of bovine growth hormone gene expression by increasing the plasmid copy number

Effect of copy number on the expression of bovine growth hormone gene (bGH) was investigated using the copy number mutants such as pKBJ10, pBJ( tet)10, pUBJ10-1, and pUBJ10 plasmids. The cells harboring plasmids below 84 copies/cell did not produced detectable levels of bGH. When the ColE1 replicon was replaced with the mutated ColE1 replicon originated from pUC19 plasmid, the copy number was increased to about 300 copies/cell and bGH production was enhanced by 11.5% (pUBJ10-1) and 12.3% of total cell protein (pUBJ10). A large amount of mRNA caused by increment of copy number would be needed to overcome some inhibitory threshold and might be an important factor for regulating bGH expression.     

Metabolic effects of developmental, tissue-, and cell-specific expression of a chimeric phosphoenolpyruvate carboxykinase (GTP)/bovine growth hormone gene in transgenic mice.

Transgenic mice were used to investigate sequences within the promoter of the gene for the cytosolic form of phosphoenolpyruvate carboxykinase (GTP) from the rat (EC 4.1.1.32) (PEPCK) which are involved in tissue-specific and developmental regulation of gene expression. Segments of the PEPCK promoter between -2000 and -109 were linked to the structural gene for bovine growth hormone (bGH) and introduced into the germ line of mice by microinjection. Bovine growth hormone mRNA was found in tissues that express the endogenous PEPCK gene, mainly in the liver but to a lesser extent in the kidney, adipose tissue, small intestine, and mammary gland. In the liver the chimeric PEPCK/bGH(460) gene was expressed in periportal cells, which is consistent with the zonation of endogenous PEPCK. The PEPCK/bGH gene was not transcribed in the livers of fetal mice until immediately before birth; at birth the concentration of bGH mRNA increased 200-fold. Our results indicate that the region of the PEPCK promoter from -460 to +73 base pairs contains regulatory sequences required for tissue-specific and developmental regulation of PEPCK gene expression. Mice transgenic for PEPCK/bGH(460) were not hyperglycemic or hyperinsulinemic in response to elevated bGH, as were transgenic mice with the MT/bGH gene. The number of insulin receptors in skeletal muscle was no different in mice transgenic for MT/bGH when compared with mice transgenic for PEPCK/bGH(460) and control animals. However, mRNA abundance for the insulin-sensitive glucose transporter in skeletal muscle was decreased in mice transgenic for the MT/bGH gene. The differences in glucose homeostasis noted with the two types of transgenic mice may be the result of the relative site of expression, the different developmental pattern, or hormonal regulation of expression of the bGH gene.     

Synthesis of bovine growth hormone by Streptomyces lividans

Streptomyces lividans 66 was transformed with a plasmid containing the regulatory region of the Streptomyces fradiae aph gene and a structural gene that specifies bovine growth hormone (bGH). When grown in liquid culture the transformant contained a protein identical to authentic bGH, as judged by radioimmunoassay and immuno-blotting (Western analysis). The bGH was present in cells that had been in culture for up to four weeks but was not found in the medium. The strategy employed should be generally applicable to the expression of foreign genes in actinomycetes.     

Evidence for Drosophila P element transposase activity in mammalian cells and yeast

Drosophila P element transposase expression is limited to the germline by tissue-specific splicing of one of its three introns. Removal of this intron by mutagenesis in vitro has allowed both P element excision and transposition to be detected in Drosophila somatic tissues. In order to determine if P element transposase can function in other organisms, we have expressed modified P elements either lacking one intron or lacking all three introns in mammalian cells and yeast, respectively. Using an assay for P element excision, we have detected apparent excision events in cultured monkey cells. Furthermore, expression of the complete P element cDNA is lethal to Saccharomyces cerevisiae cells carrying a mutation in the RAD52 gene, indicating that double-stranded DNA breaks are generated, presumably by transposase action.     

Rabbit whey acidic protein gene upstream region controls high-level expression of bovine growth hormone in the mammary gland of transgenic mice

Transgenic mice were produced which secreted high levels of bGH into milk. The 6.3-kb upstream region of the rabbit whey acidic protein (rWAP) gene was linked to the structural part of the bovine growth hormone (bGH) gene, and the chimeric gene was introduced into mouse oocytes. bGH was detected by radioimmunoassay in the milk of all resulting transgenic mice. bGH concentrations in milk varied from line to line, from 1.0–16 mg/ml. This expression was not correlated to the number of transgene copies. In all lines studied, the mammary gland was the major organ expressing bGH mRNA during lactation. bGH mRNA concentrations were barely detectable in the mammary gland of cyclic females; they increased during pregnancy. These results show that the upstream region of the rWAP gene harbors powerful regulatory elements which target high levels of bGH transgene expression to the mammary gland of lactating transgenic mice. © 1995 wiley-Liss, Inc.     

High-level expression of the bovine growth hormone gene in heterologous mammalian cells

The gene coding for bovine growth hormone (bGH) was isolated from a lambda-phage library constructed using bovine pituitary DNA partially digested with MboI. Expression of this gene transfected into mouse and monkey cells was studied. CV-1 monkey cells transfected with simian virus 40 (SV40) vectors containing the intact bGH gene, including the putative promoter region, did not express bGH. However, replacement of the bGH promoter with the mouse metallothionein-I (MT) promoter resulted in high-level synthesis and secretion of bGH. These results show that the bGH promoter functions poorly in CV-1 cells but CV-1 cells process and translate the bGH mRNA accurately. The MT-bGH chimeric gene was used to establish permanent bGH-secreting mouse C127 cell lines using the 69% transforming fragment of bovine papilloma virus (BPV) as the vector. One such cell line produced high levels of bGH and secreted it into the medium efficiently. Secreted bGH is processed accurately and is bioactive as judged by its ability to bind to rabbit liver membrane preparations.     

The use of chimeric gene constructs to express a bacterial endoglucanase in mammalian cells.

The synthesis and secretion of a truncated Clostridium thermocellum endoglucanase (EGE') encoded by the celE' gene was investigated in Chinese hamster ovary (CHO) cells. Fusion genes consisting of the human growth hormone (hGH) gene and celE', transcribed from the SV40 early enhancer/promoter, were constructed and stably transfected into CHO cells. A gene consisting of celE' inserted into the first exon of the hGH gene resulted in the synthesis of truncated proteins (less than or equal to 22 kDa) lacking endoglucanase activity. Cloning celE' into the second exon of the hGH gene, resulted in the synthesis and secretion of a 50 kDa protein with endoglucanase activity. A 50 kDa protein was also synthesised by cells transfected with celE' cloned into the fifth exon of the hGH gene. However, despite a 5-fold increase in enzyme activity compared to the exon 2 transfected cell line less than 40% of the protein was secreted. Constructs devoid of introns, in which celE' was fused to the SV40 early promoter and to the rabbit beta-globin polyadenylation sequence resulted in a 2-18-fold increase in endoglucanase activity compared to the constructs containing introns. In addition more than 75% of the synthesised protein was secreted. Analyses of EGE' encoded mRNA from the transfected cell lines suggests that the presence of introns results in the aberrant splicing of message by the use of cryptic splice sites in the celE' gene. These results demonstrate that introns are not required for the efficient expression of a bacterial endoglucanase in mammalian cells, rather introns appear to reduce expression of the encoded protein.     

Synthesis of bovine growth hormone in primates by using a herpesvirus vector.

A strain of herpesvirus saimiri containing a bovine growth hormone (bGH) gene under the control of the simian virus 40 (SV40) late-region promoter was constructed. This strain, bGH-Z20, was replication competent and stably harbored the bGH gene upon serial passage. Nonpermissive marmoset T cells persistently infected with bGH-Z20 produced a 0.9-kilobase RNA which contained all of the bGH exon sequences and appeared to initiate within the SV40 promoter region. However, in permissively infected owl monkey kidney cells, RNAs containing growth hormone sequences appeared to initiate from herpesvirus saimiri promoters positioned upstream from the SV40-growth hormone gene. Persistently infected T cells in culture secreted 500 ng of bGH protein per 10(6) cells per 24 h during the several months of testing. The secreted protein was 21 kilodaltons, the size of authentic bGH. New World primates experimentally infected with bGH-Z20 produced circulating bGH and developed immunoglobulin G antibodies directed against bGH. Because herpesviruses characteristically remain latent in the infected host, these observations suggest a means for replacing gene products missing or defective in hereditary genetic disorders.     

Instability of the plasmid carrying active penicillin acylase gene from Escherichia coli: conditions inducing insertional inactivation

Abstract The marker instability of the recombinant plasmid coding penicillin acylase production was investigated in Escherichia coli . In the absence of any selective pressure and under fully induced production of penicillin acylase the number of cells lacking plasmids increased during cultivation. Cells still harboring plasmids fully maintained their ability to synthesize the enzyme. However, when a selection for Tet^r was applied, the number of selected cells containing the actively synthesizing gene decreased. Changes occurring in plasmid DNA revealed high frequency of insertions affecting expression of penicillin acylase gene.     

促红细胞生成素基因表达载体的构建及其在CHO细胞中表达的研究

用从基因文库中所克隆的促红细胞生成素（ＥＰＯ）基因组基因,构建了３种由不同启动子调控的表达载体——ｐＯＰ１３／ＥＰＯ,ｐＲＳＶ／ＥＰＯ,ｐＣＭＶ／ＥＰＯ,在这３个表达载体的构建过程中对基因的转录起始效率、内含子的剪接、５′非翻译区和３′非翻译区对基因表达的影响等因素都加以考虑．用脂质体转染法分别将上述３个载体导入ＣＨＯ细胞,经瞬时表达,用ＥＬＩＳＡ方法检测,表达量分别为１９０ｍＩＵ／ｍｌ、１６０ｍＩＵ／ｍｌ、４４７ｍＩＵ／ｍｌ．用表达载体ｐＯＰ１３／ＥＰＯ转染ＣＨＯ－Ｋ１２细胞,在４００μｇ／ｍｌ的Ｇ４１８浓度下筛选稳定表达细胞克隆,获得了表达量约为１６０ＩＵ／１０６细胞（４８ｈ）的Ｃ１０细胞株．表达产物经Ｗｅｓｔｅｒｎｂｌｏｔ检测发现了ＥＰＯ阳性条带．用ＴＦ－１细胞对ＥＰＯ进行了生物活性检测,初步证实所表达的ＥＰＯ有生物活性．