Fig. 6.

Possible mechanistic origins of GRINS. (A) Nucleotide skews in GRINS could be generated through nucleobase tautomerism. Error-prone replication of minor tautomeric forms of G and T could result in C→T or A→G transitions in the daughter strand followed by appearance of correlated GC and TA skews after the next round of replication. Analogously, amino/imino tautomerism of C and A nucleotides would lead to opposite skews. (B) We propose that once a region of intense nucleotide skews is formed within a PKS it is more likely to undergo gene conversion between homologous module regions, thereby giving rise to GRINS.