Avirulence protein. Acts as a transcription factor in C.annuum plants. In susceptible plants lacking the Bs3 resistance gene induces expression of a number of genes, including genes homologous to a family of auxin-induced genes, alpha-expansin genes, pectate lyase, anthocyanidin glucoside rhamnosyl transferase and at least one transcription factor, UPA20. Their expression leads to plant hypertrophy in mesophyll cells, probably mainly mediated by UPA20 (PubMed:17962565). In resistant plants induces the hypersensitive response (HR), by inducing transcription of plant Bs3 which induces HR; a mutated AvrBs3 missing repeats 11-14 does not induce expression of Bs3 but does induce Bs3-E, a Bs3 allele with a modified promoter (PubMed:17962564). Binds DNA corresponding to the upa-box in sequence-specific manner. Forms a homodimer in the plant cell cytoplasm, prior to nuclear import. Interacts with the plant cell importin alpha-1 (Caimp alpha-1) and importin alpha-2 (Caimp alpha-2) via the nuclear localization signal NLS2, but not via NLS3. Secreted via type III secretion system (TTSS) (PubMed:10430949, PubMed:12366827). Localizes to the plant cell nucleus in both susceptible (bs3) and resistant (Bs3) plants (PubMed:12366827). The N-terminus is responsible for protein export from the bacteria. The central DNA-binding region is composed of 17.5 tandem core repeats with 1 base-specifying residue (BSR residue 13, also called repeat variable diresidue, RVD, residues 12 and 13) which recognizes 1 base in the target DNA; 10.5 or more repeats are required for strong gene expression (tested using an artificial TALE, PubMed:19933107). The BSR is the only residue which contacts DNA in a sequence-specific manner (PubMed:23999294). The number and order of core repeats determines its specificity for different resistance alleles in plants. Deleting and/or swapping core repeats alters the interplay between bacterial avirulence and plant resistance genes. Replacement with repeat domains from other proteins (AvrXa7 or AvrXa10 of X.oryzae pv. oryzae (AC Q56830)) does not elicit the HR in susceptible plants (PubMed:9675896). An intact NLS2 or NLS3 is required for the plant HR response, whereas NLS1 plays a minor role. Replacement of NLS1-NLS3 or NLS2-NLS3 (residues 1021-1106 or 1067-1106) with the large T-antigen NLS from the SV40 virus fully restores HR activity. The activation domain is necessary for activity in planta. By varying the BSR in each core repeat, DNA-binding domains can be generated that target specific DNA sequences and thus act as transcription factors (PubMed:19933107). By combining the central DNA-binding domain with the catalytic domain of the restriction endonuclease FokI, TALE-nuclease (TALEN) enzymes able to target specific dsDNA sequences can be created that enable eukaryotic genome modification (PubMed:20660643). Other potential uses as transcriptional repressors, for transposon targeting, DNA methylation or histone tail modifictions are also possible. Belongs to the transcription activator-like effector (TALE) family.