We have investigated putative single amino-acid InDel variants with human ESTs. Examination of the formation process for single amino-acid InDel variants indicates a possible splicing mechanism in addition to the genomic insertion/deletion events as would be expected. The wobble-splicing transcripts were often generated around the intron-exon boundaries by selecting an alternative neighboring splice signal sequence, in particular the tandem agNAG or GTNgt sequence at the splice-acceptor or -donor site, thus creating single amino-acid InDel isoforms. Another category of variants was identified with one altered amino-acid plus one amino-acid InDel, under divergent coding-frame usage. We demonstrate that such minute distance of splice site choice generates an even greater level of transcrip-tome diversity, and suggest that non-functional synonymous or intronic SNPs could be converted to functionally significant InDel alterations through this process. This subtle alteration in mRNA and protein-coding sequence may elicit a great impact upon human genome and proteome diversity. (c) 2006 Elsevier Inc. All rights reserved.