精子发生过程中基因表达转录水平的调控

哺乳动物精子发生于睾丸的生精小管, 是一个高度复杂的细胞分裂和分化过程, 涉及到错综复杂的基因表达调控过程, 包括转录和转录后水平的调控, 其中任何一个环节出错都可能导致雄性不育。因此, 揭示精子发生过程中的分子调控机理, 对发现新的男性避孕方法及治疗不育症有重要意义。文章重点综述了近年有关雄激素及其受体、雌激素及其受体、转录因子和染色质相关因子在精子发生转录水平调控的研究进展。     

Isolation of Saccharomyces cerevisiae TRP3.

Several plasmids, isolated from two plasmid pools, complemented a Saccharomyces cerevisiae trp3 mutant with defective indole-3-glycerol-phosphate synthase activity. Restriction mapping indicated that a 1.2-kilobase StuI segment was common to all complementing plasmids. Southern blot hybridization established that a cloned 5.2-kilobase BamHI fragment was derived intact from chromosomal DNA. A yeast trp3 mutant transformed with trp3-complementing plasmids contained approximately 40-fold elevated indole-3-glycerol-phosphate synthase activity. These plasmids also complemented an Escherichia coli trpC mutant, and transformants exhibited enzyme activity. Yeast trp3 is therefore associated with a 1.2-kilobase StuI DNA segment.     

Arrangement of genes TRP1 and TRP3 of Saccharomyces cerevisiae strains

The tryptophan biosynthetic genes TRP1 and TRP3 and partly also TRP2 and TRP4 have been compared by the technique of Southern hybridization and enzyme measurements in twelve wild isolates of Saccharomyces cerevisiae from natural sources of different continents, in the commonly used laboratory strain S. cerevisiae X2180-1A and in a Kluyveromyces marxianus strain. We could classify these strains into four groups, which did not correlate with their geographical distribution. In no case are the TRP3 and TRP1 genes fused as has been found in other ascomycetes. Two strains were found which, in contrast to strain X2180-1A, show derepression of gene TRP1. Two examples are discussed to demonstrate the usefulness of Southern hybridizations for the identification of closely related strains.Non-standard abbreviations InGP Indole-3-glycerolphosphate - PRA N(5-phosphoribosyl)-anthranilate     

Cloning the Cryptococcus neoformans TRP1 gene by complementation in Saccharomyces cerevisiae.

We have cloned the phosphoribosyl anthranilate isomerase (PRAI)-encoding gene (TRP1) of Cryptococcus neoformans by genetic complementation in Saccharomyces cerevisiae. Sequence analysis of this gene revealed it to be 939 bp in length, and without known promoter or termination sequences. Unlike some of the filamentous fungi, where PRAI enzymatic activity is controlled by a trifunctional gene product, the C. neoformans PRAI appears to be unifunctional. PRAI of C. neoformans exhibits 39% amino acid (aa) sequence identity compared to the S. cerevisiae counterpart. The TRP1 gene of C. neoformans maps to different size chromosomes in strains with different serotypes. The cloning of this gene for vector constructions, and the demonstration that S. cerevisiae can be used as a surrogate for C. neoformans gene expression, should help with the molecular studies of this significant fungal pathogen in our increasing immunocompromised population.     

Nucleotide sequence and functional analysis of the RAD1 gene of Saccharomyces cerevisiae.

The RAD1 gene of Saccharomyces cerevisiae is involved in excision repair of damaged DNA. The nucleotide sequence of the RAD1 gene presented here shows an open reading frame of 3,300 nucleotides. Two ATG codons occur in the open reading frame at positions +1 and +334, respectively. Since a deletion of about 2.7 kilobases of DNA from the 5' region of the RAD1 gene, which also deletes the +1 ATG and 11 additional codons in the RAD1 open reading frame, partially complements UV sensitivity of a rad1 delta mutant, we examined the role of the +1 ATG and +334 ATG codons in translation initiation of RAD1 protein. Mutation of the +1 ATG codon to ATC affected the complementation ability of the RAD1 gene, whereas mutation of the +334 ATG codon to ATC showed no discernible effect on RAD1 function. These results indicate that translation of RAD1 protein is initiated from the +1 ATG codon. Productive in-frame RAD1-lacZ fusions showed that the RAD1 open reading frame is expressed in yeasts. The RAD1-encoded protein contains 1,100 amino acids with a molecular weight of 126,360.     

Cloning and functional analysis of the ubiquitin-specific protease gene UBP1 of Saccharomyces cerevisiae

In eukaryotes, both natural and engineered fusions of ubiquitin to itself or other proteins are cleaved by processing proteases after the last (Gly76) residue of ubiquitin. Using the method of sib selection, and taking advantage of the fact that bacteria such as Escherichia coli lack ubiquitin-specific enzymes, we have cloned a gene, named UBP1, of the yeast Saccharomyces cerevisiae that encodes a ubiquitin-specific processing protease. With the exception of polyubiquitin, the UBP1 protease cleaves at the carboxyl terminus of the ubiquitin moiety in natural and engineered fusions irrespective of their size or the presence of an amino-terminal ubiquitin extension. These properties of UBP1 distinguish it from the previously cloned yeast protease YUH1, which deubiquitinates relatively short ubiquitin fusions but is virtually inactive with longer fusions such as ubiquitin-beta-galactosidase. The amino acid sequence of the 809-residue UBP1 lacks significant similarities to other known proteins, including the 236-residue YUH1 protease. Null ubp1 mutants are viable, and retain the ability to deubiquitinate ubiquitin-beta-galactosidase, indicating that the family of ubiquitin-specific proteases in yeast is not limited to UBP1 and YUH1.     

Cloning and functional analysis of the arginyl-tRNA-protein transferase gene ATE1 of Saccharomyces cerevisiae

Aminoacyl-tRNA-protein transferases (Arg-transferases) catalyze post-translational conjugation of specific amino acids to the amino termini of acceptor proteins. A function of these enzymes in eukaryotes has been shown to involve the conjugation of destabilizing amino acids to the amino termini of short-lived proteins, these reactions being a part of the N-end rule pathway of protein degradation (Gonda, D. K., Bachmair, A., Wünning, I., Tobias, J. W., Lane, W. S., and Varshavsky, A. (1989) J. Biol. Chem. 264, 16700-16712). We have cloned the ATE1 gene of the yeast Saccharomyces cerevisiae which encodes arginyl-tRNA-protein transferase. ATE1 gives rise to a approximately 1.6-kilobase mRNA and codes for a 503-residue protein. Expression of the yeast ATE1 gene in Escherichia coli, which lacks Arg-transferases, was used to show that the ATE1 protein possesses the Arg-transferase activity. Null ate1 mutants are viable but lack the Arg-transferase activity and are unable to degrade those substrates of the N-end rule pathway that start with residues recognized by the Arg-transferase.     

A functional analysis of the Candida albicans homolog of Saccharomyces cerevisiae VPS4

To investigate the role of the prevacuolar secretion pathway in the trafficking of vacuolar proteins in Candida albicans, the C. albicans homolog of the Saccharomyces cerevisiae vacuolar protein sorting gene VPS4 was cloned and analyzed. Candida albicans VPS4 encodes a deduced AAA-type ATPase that is 75.6% similar to S. cerevisiae Vps4p, and plasmids bearing C. albicans VPS4 complemented the abnormal vacuolar morphology and carboxypeptidase missorting in S. cerevisiae vps4 null mutants. Candida albicans vps4Delta null mutants displayed a characteristic class E vacuolar morphology and multilamellar structures consistent with an aberrant prevacuolar compartment. The C. albicans vps4Delta mutant degraded more extracellular bovine serum albumin than did wild-type strains, which implied that this mutant secreted more extracellular protease activity. These phenotypes were complemented when a wild-type copy of VPS4 was reintroduced into its proper locus. Using a series of protease inhibitors, the origin of this extracellular protease activity was identified as a serine protease, and genetic analyses using a C. albicans vps4Deltaprc1Delta mutant identified this missorted vacuolar protease as carboxypeptidase Y. Unexpectedly, C. albicans Sap2p was not detected in culture supernatants of the vps4Delta mutants. These results indicate that C. albicans VPS4 is required for vacuolar biogenesis and proper sorting of vacuolar proteins.     

Heat stress regulates the expression of TPK1 gene at transcriptional and post-transcriptional levels in Saccharomyces cerevisiae

In Saccharomyces cerevisiae cAMP regulates different cellular processes through PKA. The specificity of the response of the cAMP-PKA pathway is highly regulated. Here we address the mechanism through which the cAMP-PKA pathway mediates its response to heat shock and thermal adaptation in yeast. PKA holoenzyme is composed of a regulatory subunit dimer (Bcy1) and two catalytic subunits (Tpk1, Tpk2, or Tpk3). PKA subunits are differentially expressed under certain growth conditions. Here we demonstrate the increased abundance and half-life of TPK1 mRNA and the assembly of this mRNA in cytoplasmic foci during heat shock at 37 °C. The resistance of the foci to cycloheximide-induced disassembly along with the polysome profiling analysis suggest that TPK1 mRNA is impaired for entry into translation. TPK1 expression was also evaluated during a recurrent heat shock and thermal adaptation. Tpk1 protein level is significantly increased during the recovery periods. The crosstalk of cAMP-PKA pathway and CWI signalling was also studied. Wsc3 sensor and some components of the CWI pathway are necessary for the TPK1 expression upon heat shock. The assembly in foci upon thermal stress depends on Wsc3. Tpk1 expression is lower in a wsc3? mutant than in WT strain during thermal adaptation and thus the PKA levels are also lower. An increase in Tpk1 abundance in the PKA holoenzyme in response to heat shock is presented, suggesting that a recurrent stress enhanced the fitness for the coming favourable conditions. Therefore, the regulation of TPK1 expression by thermal stress contributes to the specificity of cAMP-PKA signalling.     

Construction of a human cytochrome c gene and its functional expression in Saccharomyces cerevisiae

The nucleotide sequences of a partial cDNA and three pseudogenes of human cytochrome c were determined. The complete nucleotide sequences which encode human cytochrome c were constructed on the basis of one of the pseudogenes by in vitro mutagenesis. The constructed human cytochrome c was functionally expressed in Saccharomyces cerevisiae. The recombinant human cytochrome c was purified and characterized.