Improving the mutagenesis efficiency of the Kunkel method by codon optimization and annealing temperature adjustment

The Kunkel method is a widely used site-directed mutagenesis strategy that introduces point mutations by annealing mutation-containing oligonucleotides to single-stranded uracil-containing DNA (dU-ssDNA) templates. The method is fast and inexpensive and has been routinely employed to generate point mutations and multi-site mutations. However, its efficiency for point mutations is highly variable. In this work, codons in both DNA templates and mutagenic oligonucleotides were optimized to lower the GC percentage (GC%) of the complementary regions, and the oligonucleotide length was also extended to reduce the GC difference between upstream and downstream regions. These modifications largely increased the mutation efficiency of single-site mutagenesis. In addition, a multi-stage cooling programme was developed in the annealing step specifically for multi-site mutagenesis, which increased the simultaneous mutation efficiency. The modifications will help in generating antibody libraries by effectively randomizing multiple CDRs simultaneously.

tRNA diversification among uncultured archeon clones

Whole genome sequences (DNA sequences) of four uncultured archeon clones (1B6:CR626858.1, 4B7:CR626856.1, 22i07:JQ768096.1 and 19c08:JQ768095.1) were collected from NCBI BioSample database for the construction of digital data on tRNA. tRNAscan-SE 2.0 and ENDMEMO tools were used to identify and sketch tRNA structure as well as calculate Guanine-Cytosine (GC) percentage respectively. Eight true/functional tRNAs were identified from above 4 sequences which showed cove score greater than 20% with no variable loop. The tRNAs from the uncultured archeon clones were classified as Ala, Arg, Ile, Thr, Pro and Val type tRNA with cove score ranging from 34.22%-79.03%. The range of GC content was found 42.89%-56.91%; while tRNA contributed GC content ranging from 52%-64.86% to the total GC content in these sequences. The data fabricated in this study could be very useful for studying the diversity of tRNA among prokaryotes.