A human PAC (PAC671D9) containing only the MECP2 locus and regulatory elements was modified to introduce a R111G (AGG to GGG) missense mutation in the methyl-CpG binding domain (MPD) of exon 3 and a C-terminal GFP tag. Expression of the transgene parallels that of endogenous MECP2 in the brain. (J:214143)