Mapping of regions on cloned Saccharomyces cerevisiae 2-mum DNA coding for polypeptides synthesized in Escherichia coli minicells

Curing of Saccharomyces cerevisiae 2-μm DNA by transformation

A general procedure for the curing of 2-μm in Saccharomyces cerevisiae is described. The method is based on the displacement of endogenous 2-μm DNA by the recombinant plasmid pMP78-1, which carries the yeast leu2 gene and the 2 -μm DNA replicon, but cannot be maintained stably in a yeast cell without endogenous 2-μm DNA. After transformation with pMP78-1 cells are grown selectively to displace 2-μm DNA. During the non-selective growth which follows, plasmid pMP78-1 is lost and up to 100% of the cells completely lack plasmids. In conjunction with a kanamycin resistance marker, as present in plasmid pMP81, this method should be applicable to cure any wild-type yeast strain. The stability of recombinant plasmids in cir (+) and cir (0) strains has been compared.

Detection of a 2 mu derivative yeast plasmid with altered properties

The Saccharomyces cerevisiae (Sacch. cerevisiae) strain RXII, like many others, harbours plasmid DNAs. and one category of them is homologous to the 2 mu plasmid of yeast. DNA-DNA hybridization experiments indicated altered structures of this species as regards the number and distribution of the restriction sites. The efforts made to clone either the whole plasmid in pBR328 or its fragments in pBR322 vectors remained unsuccessful, since deleted plasmids were isolated without insert DNA, and even the loss of vector sequences was observed. The data suggest, that the 2 mu derivative plasmid in strain RXII represent an unique category of this extrachromosomal genetic element.

Expression of recombinant DNA functional products in Escherichia coli anucleate minicells

This review covers the use of anucleate minicells of Escherichia coli for expressing the recombinant DNA encoded proteins. We briefly discuss the methods being used for preparation of anucleate minicells, incorporation of cloned DNA and assessment of gene expression. While the largest use has been that of microbially derived cloned functional DNA, examples of eukaryotic gene product synthesis have also been reviewed. This technology may represent some interesting commercial opportunities.

Yeast plasmid requires a cis-acting locus and two plasmid proteins for its stable maintenance

Unstable ars1 (autonomously replicating sequence)-containing plasmids can be stabilized by connecting particular DNA segments of yeast 2 mu-plasmid. A cis-acting locus for the plasmid's stability (the STB locus) was found in the large unique region and separated from the replication origin of 2 mu-plasmid. Several direct repeats found in this region were essential for its function. Two proteins encoded by the plasmid (B and C) were required as trans-acting factors. The average copy number of the plasmid was not affected whether the plasmid carried the stability system or not, suggesting that the system was not directly associated with the replication function but was involved in partitioning at cell division.

Topological modifications and template activation are induced in chimaeric plasmids by inserted sequences

The effect of the insertion of foreign genes or gene systems in closed DNA domains has been investigated in vitro in purified systems. We observe that in chimaeric plasmids two apparently independent classes of modifications, (1) functional and (2) topological, do take place in defined instances. (1) Among the screened yeast gene systems, examples have been found of DNA sequences that upon insertion cause activation of in vitro transcription of distant genes. (2) Foreign DNA sequences may lead to new topological features of the harbouring plasmids; it is shown that more than one S1-sensitive secondary structure may be contemporaneously present on the same chimaeric plasmid. DNA superhelicity is a prerequisite of these modifications. The two classes of effects (1) functional and (2) topological are not a priori directly related one to the other but appear to be two independent consequences of the same cause: the insertion of foreign DNA sequences into closed DNA domains. These observations suggest a regulatory model of gene expression based on alternative topologies of closed DNA domains.

Synthesis of Escherichia coli outer membrane ompA protein in yeasts

Saccharomyces cerevisiae was transformed with the Escherichia coli ompA gene coding for an outer membrane protein. Yeast transformants containing the pYTU101 plasmid, consisting of the ompA gene cloned in pSC101 and the HindIII-3 fragment of 2-microns DNA, express the foreign membrane protein. The protein synthesized in yeast has an Mr value very similar if not identical to that of the mature E. coli protein. The expressed protein is present in yeast mitochondrial and plasma membrane fractions. The yeast cell can tolerate about 250 molecules of the foreign membrane protein per cell, although the transformants show altered growth kinetics.

In vitro transcription by purified yeast RNA polymerase II. Coarse promoter mapping on homologous cloned genes

Clones of the yeast Tyl element and 2 microns plasmid have been selectively transcribed in vitro by partially or completely purified yeast RNA polymerase II. Electrophoretic analysis of whole and restricted ternary transcription complexes allows the localization of the in vitro actively transcribed regions of the analyzed genes. The DNA regions that actively promote in vitro transcription correspond to the nucleotide sequence that in the Tyl element encompasses the in vivo transcription initiation sites and that in the 2 micrometer plasmid encompasses the starting codons of two oppositely oriented potential protein coding frames. The transcription assay that we describe herein may be applied to analyze rapidly the in vitro transcription of clones genes, to localize transcription initiation sites on supercoiled templates and to evaluate the differential in vitro promoter strength in RNA polymerase II served genes. Data obtained with RNA polymerase II at two different stages of purification are presented in parallel. Studies with a completely purified enzyme should certainly be preferred although the use of a partially purified RNA polymerase II may be convenient and may reveal factors which affect specificity.

Recombination within the yeast plasmid 2mu circle is site-specific

The multicopy yeast plasmid, 2mu circle, encodes a specialized recombination system. It contains two regions, each 599 bp in length, that are precise inverted repeats of each other and between which recombination occurs readily. In addition, this recombination requires the product of a 2mu circle gene, designated FLP. By examining the products of FLP-mediated recombination of plasmids containing single insertions within one of the repeated regions, we show that this recombination occurs only at a specific site within the repeat. This result was confirmed from analysis of the ability of plasmids containing various deletions within one of the repeated regions to serve as substrates for FLP-mediated recombination. These experiments limit the recombination site to a sequence of less than 65 bp. In addition, by mutational analysis of the recombination potential of a hybrid plasmid containing the entire 2mu circle genome, we have shown that FLP is only the 2mu circle gene necessary for this site-specific recombination. Finally, we describe a sensitive assay for recombination between the repeated sequences of 2mu circle; using it, we demonstrate that even in the absence of FLP gene product, recombination between the repeats occurs at a low but detectable level during meiosis.

Selective in vitro transcription by purified yeast RNA polymerase II on cloned 2 micron DNA

The in vitro transcription properties of purified yeast RNA polymerase II have been analyzed on prokaryotic plasmids (pBR322 and pBR313) and chimaeric plasmids bearing yeast 2 micron sequences (BTYP 1, BTYH 2 and BTYH 3). Conditions for selective transcription of the 2 micron DNA sequences in chimaeric plasmids have been determined. pBR322 and pBR313 are not transcribed by the purified RNA polymerase II when not bearing eukaryotic inserts. We show that the agarose gel electrophoretic analysis of ternary transcription complexes allows the localization of nascent RNA chains. The RNA produced has been visualized by electron microscopy (nascent RNA hybridization loops) and by gel electrophoretic analysis. All the observed properties are shared by RNA polymerase II purified by a conventional method (1) and by a rapid alternative procedure described herein. The peculiar properties of a partially purified form of RNA polymerase II are reported.

DNA synthesis catalyzed in vitro by yeast extracts

A procedure to prepare crude extracts from single colonies of Saccharomyces cerevisiae is described. Partially purified extracts catalyzed DNA synthesis directed by single-stranded fd DNA. Maximum activity requires the presence of ribonucleoside triphosphates although extensive DNA synthesis is observed in the presence of only deoxynucleoside triphosphates. Alkaline sucrose gradient analysis demonstrated that initiation of new DNA chains occurs in vitro and the DNA products synthesized are heterogeneous in size, Isopycnic analysis of the products of ribonucleotide-initiated fd DNA replication showed covalent linkage between the initiator RNA and the newly synthesized DNA. The fd-replicating capacity of extracts prepared from cell-division-cycle mutants, defective in events controlling DNA initiation of elongation, showed an increased thermosensitivity in the DNA replication reaction in vitro.

Expression and processing of bacterial beta-lactamase in the yeast Saccharomyces cerevisiae

The mode of expression in Saccharomyces cerevisiae of the bacterial antibiotic resistance gene coding for beta-lactamase (EC 3.5.2.6) is described. Yeast transformants, containing hybrid plasmid pMP78-1 consisting of pBR325 in a 2-micrometers DNA vector, synthesize an active beta-lactamase protein. The enzyme was purified about 100-fold over crude extracts. With regard to activity, molecular weight, and binding to specific antibodies the yeast beta-lactamase was indistinguishable from the purified enzyme from Escherichia coli. Because the bacterial enzyme is synthesized as a preprotein with subsequent maturation, the results suggest that S. cerevisiae is able to convert the preprotein to the mature beta-lactamase. This was confirmed by in vitro experiments showing that the bacterial preprotein can be processed by crude extracts of S. cerevisiae.

Replication and recombination functions associated with the yeast plasmid, 2 mu circle

By examining both the transformation efficiency of yeast of various plasmids containing defined regions of the 2 mu circle genome and the characteristics of the resultant transformants, we have identified several regions of the 2 mu circle genome which are involved in 2 mu circle replication or recombination. First, by identifying those DNA fragments from the molecule which promote high frequency transformation of yeast, we have localized the origin of replication to a sequence partially within the large unique region, which, as determined by subsequent deletion analysis, extends from the middle of the inverted repeat region into the contiguous unique region. Second, by examining the relative efficiency of replication in yeast of hybrid plasmids containing either the entire 2 mu circle genome or a fragment of 2 mu circle encompassing the origin of replication, we have determined that efficient use of the 2 mu circle origin requires some function or functions encoded in the molecule at a site away from the origin. Third, by examining the ability of a mutant 2 mu circle molecule to undergo intramolecular recombination in yeast, we have identified a 2 mu circle gene which codes for a product required for this process.

Nucleotide sequence of the yeast plasmid

The nucleotide sequence of the yeast DNA plasmid (2 mu circle) from Saccharomyces cerevisiae strain A364A D5 has been determined. The plasmid contains 6,318 base pairs, including two identical inverted repeats of 599 base pairs. Possible functions are suggested, and attributes of an improved vector for cloning foreign DNAs in yeast are discussed.

Saccharomyces cerevisiae plasmid, Scp or 2 mum: intracellular distribution, stability and nucleosomal-like packaging

Cell fractions from yeast strains known to harbor the plasmic 2 mum or Scp were treated with nucleases used to probe eukaryotic chromosome structure. Scp and subfragments were identified by hybridization to natural or cloned Scp probes according to Southern (34). Specificity was confirmed with non-Scp probes. Copy/haploid nuclear genome(n) was estimated from reconstructions at a resolution of 0.5/n. About 43-67% of the total cellular copy exists as nucleoprotein complexes which separate from other debris on isokinetic sucrose gradients with s-values of 67-110. These complexes are totally degraded by DNAase I. Digestion with micrococcal nuclease produced integral-sized fragments; they are not generated by direct mixing of pure Scp with nuclear chromatin from a[cir] strain. Initial digests gave a repeat of 168 +/- 3 base pairs (bp) for both Scp and nuclear nucleoprotein; advanced digests reduced the nuclear repeat relative to Scp by 8 bp. Of a potential 37 repeat units/plasmid, 31-32 were directly measured. A strain difference in Scp autodegradation was found. A partial nuclease resistant form was also demonstrated whose abundance was cell strain and growth stage dependent. Both Scp isomers exist in these complexes which are structurally similar to simian viral 40 minichromosomes.

Identification and mapping of the transcriptional and translational products of the yeast plasmid, 2mu circle

We have identified two major and approximately ten minor poly(A)-containing RNA species in S. cerevisiae which arise from in vivo transcription of the yeast plasmid, known as 2mu circle. The two major species, which are 1325 and 1275 bases in length, are transcribed from the two unique halves of the plasmid and extend into the inverted repeat sequences which separate the unique regions. The map positions of the minor transcripts, which range in length from 350 to 2600 bases, indicate that except for a small region of the genome in which no transcription is observed, both strands of the entire 2mu circle genome are transcribed. We also present evidence demonstrating that RNA transcribed from 2mu circular DNA is used to program the synthesis of specific proteins in yeast: that is, yeast RNA complementary to 2mu circle DNA can be translated in vitro to produce specific polypeptides of substantial size. Finally, the pattern of transcription of 2mu circle suggests the possibility that messenger RNA species are derived by cleavage of larger transcripts, and in addition, that the intramolecular recombination of 2mu circle which occurs in yeast functions as a genetic switch to allow separate expression of two sets of genes on the 2mu circle genome.