Microexon-based regulation of ITSN1 and Src SH3 domains specificity relies on introduction of charged amino acids into the interaction interface

► Splicing of microexons regulates structure of the SH3 domains of ITSN1 and Src. ► Microexons of ITSN1 and Src genes are conserved in vertebrates. ► ITSN1 transcripts with microexon are detected upon appearance of neurons in embryos. ► Microexon-encoded insertions alter charged residues distribution in the SH3 domains.