DNA sequence and functional analysis of an ARS-element from the zygomycete Absidia glauca

A homologous and self-replicating system for efficient transformation of Fusarium oxysporum

A highly efficient transformation system has been developed for Fusarium oxysporum f. sp. lycopersici based on the complementation of a nitrate-reductase mutant with the homologous nit1 gene and on the presence of ARS and telomeric sequences in the vector. Preliminary transformation experiments with the niaD gene from Aspergillus niger generated self-replicating plasmids within the transformed entity that contained extra-fungal DNA. A fragment of the extra DNA was inserted into pUC19 together with the F. oxysporum nit1 gene, resulting in plasmid pFNit-Lam. This allowed the isolation of a new linear plasmid within self-replicative F. oxysporum transformants (pFNit-Lam-TLam, linear). The circular form of this vector yielded 5600 fungal transformants per microgram of DNA. All of the transformants contained autonomous linear plasmids harboring direct repeats of fungal DNA at both ends. The sequence of the 1.2-kb fragment from F. oxysporum responsible for autonomous replication, and maintenance as linear plasmid molecules, has been determined. Comparison analysis with the ARS from different organisms has shown that this fragment contained the commonly identified ARS consensus sequence, 5'A/TTTTATA/GTTTA/T3' and, in addition to this core, ten copies of the ARS-box, 5'TNTA/GAA3'. Adjacent to this presumed ARS, the telomeric hexanucleotide sequence (TTAGGG)n was present in six tandem copies followed by 18 copies of its complementary sequence.

Sequence analysis of a Papaver somniferum L. mitochondrial DNA fragment promoting autonomous plasmid replication in Saccharomyces cerevisiae and Kluyveromyces lactis

The minimal fragment of mitochondrial DNA from Papaver somniferum L. (poppy) able to promote autonomous plasmid replication in the yeast Saccharomyces cerevisiae was sequenced. Sequence analysis of the 917-bp MK4/8 DNA fragment revealed a high AT content, and the presence of two 12-bp sequences differing from the ARS core consensus of S. cerevisiae only by a T and C insertion, respectively. The mitochondrial insert contains a further six 11-bp sequences with one mismatch to the S. cerevisiae core consensus, more then 20 related sequences with two base pair exchanges, numerous direct and inverted repeats, and many copies of a sequence motif called the ARS box. The original 4.2-kb mitochondrial DNA fragment, as well as the minimal 917-bp subfragment in vector pFL1-E (a variant of YIP5, lacking an origin of replication in yeast), were then tested for their ability to replicate autonomously in another fungus, Kluyveromyces lactis.

Heterologous transformation of Mucor circinelloides with the Phycomyces blakesleeanus leu1 gene

The leu1 gene of Phycomyces blakesleeanus was isolated within a HindIII-HindIII genomic DNA fragment by heterologous hybridization screening of a cosmid library, making use of the Mucor circinelloides leuA gene as a probe. The complete nucleotide sequence of this fragment reveals a single 2070 bp ORF with no introns, which presents at least 68% homology with that of the leuA gene. The P. blakesleeanus leu1 gene has also been expressed in the M. circinelloides mutant R7B (leu-), which was used to isolate the leuA gene by complementation. The homology with other known sequences shows that the leu1 gene encodes the P. blakesleeanus alpha-IPM (isopropylmalate) isomerase.

Integrative transformation by homologous recombination in the zygomycete Mucor circinelloides

Transformation of a Mucor circinelloides Leu- strain with the plasmid pAD45, harbouring the wild-type allele (leuA+) and a chymosin gene, led to the identification of mitotically stable transformants after one to three vegetative growth cycles on non-selective medium. Southern analysis of the stable transformed strains demonstrated that the vector is integrated, as an intact molecule, into the resident Mucor leuA locus. Retransformation of Escherichia coli with genomic DNA restricted with enzymes having no or only a single recognition site within the inserted sequence did not permit isolation of plasmids or fragments carrying the leuA or chymosin gene.