Organization of the 5.8S, 16?18S, and 23?28S ribosomal RNA genes of Cephalosporium acremonium

An electrophoretic molecular karyotype for an industrial strain of Cephalosporium acremonium

An electrophoretic molecular karyotype has been established for an industrial strain of Cephalosporium acremonium using transverse alternating field electrophoresis. Eight chromosome bands were detected in gently prepared DNA samples. The size of the chromosomes ranged from approx. 1700 kb up to greater than 4000 kb. The total genomic content for this strain of C. acremonium is at least 22,500 kb. Hybridization analyses revealed that two key genes involved in cephalosporin C biosynthesis are not physically linked to one another. The isopenicillin N synthetase gene (pcbC) resides on chromosome (chr.) VI while the deacetoxycephalosporin C synthetase/deacetylcephalosporin C synthetase gene (cefEF) resides on chr. II. The ribosomal RNA genes were located on chr. VII, while the beta-isopropylmalate dehydrogenase gene (LEU2) was found to be linked to the pcbC gene on chr. VI.

Organization of ribosomal RNA genes in the fungus Cochliobolus heterostrophus

The genes encoding the 17S, 5.8S and 25S ribosomal RNAs in the Ascomycete Cochliobolus heterostrophus were cloned and analyzed. They are arranged in tandemly repeated units (rDNA) either 9.0 or 9.15 kilobases in length, depending upon the strain. The 5S rRNA genes are not part of the tandemly repeated rDNA. Instead, many and perhaps all of the 5S genes are dispersed in the genome, as they are in the fungi Neurospora, Aspergillus and Schizosaccharomyces. Comparative restriction maps of the rDNA from C. heterostrophus and other filamentous fungi and yeasts are presented. A survey of rDNAs from twenty-three field isolates of C. heterostrophus collected worldwide demonstrated that each isolate has one or the other of two rDNA forms, which differ in length and in the presence or absence of at least three restriction enzyme sites. The differences are all located in spacer DNA outside the coding regions for the rRNA genes. Heterogeneity in the rDNA repeat was not observed within any single isolate. The copy number of the rRNA gene cluster in C. heterostrophus is approximately 130 per haploid genome.

Efficient integrative transformation of Cephalosporium acremonium

A hybrid gene, IPNSp/HPTorf, was constructed by placing an 850 bp sequence of Cephalosporium acremonium DNA next to the 5' end of a bacterial open reading frame, HPTorf. The sequence was obtained as an 850 bp NcoI restriction fragment from the 5' non-coding region of the C. acremonium isopenicillin N synthetase (IPNS) gene. The HPTorf was obtained from a bacterial gene that coded for a hygromycin B phosphotransferase (HPT). Plasmids that contained IPNSp/HPTorf transformed C. acremonium to a stably maintained hygromycin B resistant phenotype. Southern analysis of total DNA from transformants demonstrated multiple integrations of the transforming DNA in the high molecular weight DNA of most transformants, but single integrations were observed in a few transformants. The number of transformants per microgram of DNA was about 100 times greater than for plasmids that contained the HPTorf without any juxtaposed eucaryotic promoter sequence. Plasmids with the promoterless HPTorf and plasmids with a truncated S. cerevisiae phosphoglycerate kinase promoter juxtaposed to the HPTorf transformed C. acremonium at equivalent low frequencies. Transformation of C. acremonium with linearized plasmid DNA produced at least 2-3 fold more transformants than the corresponding circular molecule. Several observations were made concerning protoplast formation and handling which made the transformation procedure more efficient and allowed a greater proportion of protoplasts to regenerate to viable walled cells. Plasmids were constructed that contained both the IPNSp/HPTorf and additional elements: fragments of C. acremonium ribosomal DNA (rDNA), or a fragment of C. acremonium mitochondrial DNA possessing activity as an autonomous replication sequence (ARS) in S. cerevisiae, or putative transcriptional termination/polyadenylation signals from the IPNS gene. These plasmids transformed C. acremonium at frequencies experimentally equivalent to those containing IPNSp/HPTorf without any of these additional elements.