Hygromycin- and paromomycin-resistant mutants of Aspergillus nidulans alter translational fidelity

An efficient shortened genetic transformation strategy for filamentous fungus Trichoderma reesei

The filamentous fungus Trichoderma reesei is one of the most important fungi for the production of cellulases and xylanases, which can be used for biofuel production from lignocellulose. We aimed to develop an effective selection marker system for more extensive functional genomic studies in the fungus T. reesei, and to construct better industrial transformants for producing cellulases. Here, we present a novel effective G418 selection marker to use a codon-optimized neomycin phosphotransferase II gene nptII to transform T. reesei. We developed an effective and erasable selection marker, lcNG, and a combined genetic transformation system for gene manipulation in T. reesei using a two-Agrobacterium-mediated transformation method. This transformation strategy combines two steps in the transformation protocol, which saves 15-30-day's time. The system could be a useful tool for the genetic engineering of T. reesei.

Multiple defects in translation associated with altered ribosomal protein L4

The ribosomal proteins L4 and L22 form part of the peptide exit tunnel in the large ribosomal subunit. In Escherichia coli, alterations in either of these proteins can confer resistance to the macrolide antibiotic, erythromycin. The structures of the 30S as well as the 50S subunits from each antibiotic resistant mutant differ from wild type in distinct ways and L4 mutant ribosomes have decreased peptide bond-forming activity. Our analyses of the decoding properties of both mutants show that ribosomes carrying the altered L4 protein support increased levels of frameshifting, missense decoding and readthrough of stop codons during the elongation phase of protein synthesis and stimulate utilization of non-AUG codons and mutant initiator tRNAs at initiation. L4 mutant ribosomes are also altered in their interactions with a range of 30S-targeted antibiotics. In contrast, the L22 mutant is relatively unaffected in both decoding activities and antibiotic interactions. These results suggest that mutations in the large subunit protein L4 not only alter the structure of the 50S subunit, but upon subunit association, also affect the structure and function of the 30S subunit.

Development of Spontaneous Hygromycin B Resistance in Monilinia fructicola and Its Impact on Growth Rate, Morphology, Susceptibility to Demethylation Inhibitor Fungicides, and Sporulation

ABSTRACT Agrobacterium tumefaciens-mediated transformation with plasmids carrying the hygromycin B resistance gene hph frequently is being used for inserting genes into fungal spores and mycelial cells and for conducting insertional mutagenesis to identify genes connected to a particular phenotype. In this article, we report that stable hygromycin B resistance can develop spontaneously in germinating conidia from Monilinia fructicola and that the mutants exhibit altered phenotypes. One spontaneously developing hygromycin B-resistant colony developed per 2.5 x 10(5) germinating conidia. Mutants grew significantly slower on potato dextrose agar, were 2.4- to 3.1-fold more sensitive to demethylation inhibitor fungicides, lacked melanization, and did not produce spores. The mode of action of hygromycin B resistance in the mutants seemed to be different from the hph transgene-mediated hygromycin B resistance based on different phenotypic characters. The ability of M. fructicola and possibly other fungi to spontaneously develop hygromycin B resistance associated with an altered phenotype may interfere with the selection of true transformants if hygromycin B is used as selective agent. This is particularly confounding if the hph gene is used as selectable marker in insertional mutagenesis experiments conducted for the identification of genes involved in melanization, sporulation, or fungicide resistance.

Nonsense suppressor and antisuppressor mutations at the 1409-1491 base pair in the decoding region of Escherichia coli 16S rRNA

Using a genetic selection for suppressors of a UGA nonsense mutation in trpA, we have isolated a G to A transition mutation at position 1491 in the decoding region of 16S rRNA. This suppressor displayed no codon specificity, suppressing UGA, UAG and UAA nonsense mutations and +1 and -1 frameshift mutations in lacZ. Subsequent examination of a series of mutations at G1491 and its base-pairing partner C1409 revealed various effects on nonsense suppression and frameshifting. Mutations that prevented Watson-Crick base pairing between these residues were observed to increase misreading and frameshifting. However, double mutations that retained pairing potential produced an antisuppressor or hyperaccurate phenotype. Previous studies of antibiotic resistance mutations and antibiotic and tRNA footprints have placed G1491 and C1409 near the site of codon-anticodon pairing. The results of this study demonstrate that the nature of the interaction of these two residues influences the fidelity of tRNA selection.