The entire DNA sequence of chromosome III of the yeast Saccharomyces cerevisiae has been determined. This is the first complete sequence analysis of an entire chromosome from any organism. The 315-kilobase sequence reveals 182 open reading frames for proteins longer than 100 amino acids, of which 37 correspond to known genes and 29 more show some similarity to sequences in databases. Of 55 new open reading frames analysed by gene disruption, three are essential genes; of 42 non-essential genes that were tested, 14 show some discernible effect on phenotype and the remaining 28 have no overt function.

A p tubulin gene of Physarum polycephalum has been isolated from a genomic library in the phage EMBL4.Southern-blot hybridization to genomic DNA indicates that the cloned DNA is derived from the betB1 locus of the p tubulin gene family. A tubulin-specific subfragment of the phage DNA was used as a hybridization probe to construct a restriction map of the betBI locus. The probe consisted of the almost complete coding region of the 5' half of the tubulin gene, interrupted by one intron. The derived amino acid sequence of this subclone deviates from the protein sequence for Physarum amoebal p tubulin (amino acids 4-207) in two of 207 amino acids. We used both recA and recBC sbcB bacterial host strains, which have been recommended for cloning of instability-conferring sequences of the Physarum genome, but were unable to subclone the 3' part of the gene from the phage DNA. Primer-extension analysis indicates that the betB gene is expressed in the vegetatively proliferating amoebal and plasmodia1 stages of the life cycle as well as in differentiating (sporulating) plasmodia.In uninucleate myxamoebae of Physarum polycephalum microtubuli serve varied functions as components of the cytoskeleton, of the flagella and in the mitotic spindle. In multinucleate plasmodia, on the other hand, microtubuli are used only in the closed mitotic spindle [l]. Surprisingly, twodimensional electrophoresis resolves tubulins into al and p1 isotypes in amoebae, and a l , a2, PI, pz isotypes in plasmodia [2]. Recent studies show that these electromorphs are composed of different subspecies [3, 41 at least some of which are encoded by distinct genes. While cloning and analysis of the LY tubulin genes and their expression are in progress [5], the analysis of p tubulin genes and their expression is hampered by a lack of cloned p tubulin sequences. The futility of attempts of various laboratories to isolate / 3 tubulin genes has been attributed to an instability of cloned p tubulin genes caused by internal repetitive sequences [6]. In spite of the considerable efforts of various laboratories, the number of cloned Physarum genes is still very limited. The problems encountered in the cloning of genomic DNA may be due to the occurrence of repetitive sequences throughout the genome that lead to the formation of hairpin structures. These can be visualized in the electron microscope at regular intervals of approx. 7 kb [7]. Formation of such hairpin structures might interfere with the replication of recombinant cloning vectors. Recently Nader and coworkers [8] demonstrated that part of the Physarum genome can be stably cloned only in recBC sbcB bacterial host strains. These authors identified a small fragment of 360 bp that conferred instability to a cloned actin gene, in recA host strains.Here we report the cloning of a Physarum p tubulin gene. recombinant EMBL4 phage. Southern-blot hybridization, DNA sequence and expression analysis suggest that the cloned DNA is derived from the betB locus. Subcloning and analysis of the 3' half of the gene has not...

Photo-induced fruiting-body formation of the slime mold Physarum polycephalum can be divided into two stages. The first stage (I) starts with the beginning of illumination (0 h) and ends with the formation of nodules (12 h). The second stage (II) is characterized by culmination, sporangiophore formation and melanization of sporangiophore heads (13-17 h). We investigated the expression of actin, alpha- and beta-tubulin during this differentiation process using Northern blot analysis and run-off transcription in isolated nuclei. Whereas actin mRNA is irreversibly lost during stage I, we observed two peaks in mRNA concentration for alpha-tubulin and one peak for that of beta-tubulin during stage I and a coordinated alpha/beta-tubulin mRNA induction during stage II. Stage II induction appears to be related to a presporangial mitosis. Transcriptional activity of the three genes studied shows two maxima, namely one in the middle of stage I and the other at the end of stage II. Our data suggest that the expression of the three cytoskeletal proteins investigated follows a distinct temporal pattern comprising changes in both mRNA synthesis and decay. We also propose a novel function of tubulin in Physarum which is not related to mitosis.

A natural plasmid, pSAR1, was isolated from the antibiotic producer Streptomyces arenae TÜ469. Its size is estimated to approx. 80 kbp by restriction analysis. pSAR1 occurs in two copy‐number states differing by a factor of at least 10, depending on culture conditions. The hifh copy‐number state is strongly correlated with the production of the antibiotic pentalenolactone. The decrease of copy numbers after change of culture conditions is completed within 1 h. These unusually rapid kinetics and the occurrence of degradational intermediates suggest the participation of specific catalytic mechanisms in copy number regulation.