Amino acid sequence similarity between HPV16/18 E1s. (A) The amino acid sequence alignment between HPV16/18 E1s using MAFFT . Identical residues are indicated with asterisks (*). Highly conserved residues are indicated with colons (:). Semi-conserved residues are indicated with periods (.). (B) The amino acid sequence identities of the ND (amino acids 1 to 190 of HPV16 E1 and 1 to 197 of HPV18 E1), DBD (amino acids 191 to 352 of HPV16 E1 and 198 to 359 of HPV18 E1), OD (amino acids 353 to 430 of HPV16 E1 and 360 to 437 of HPV18 E1), HD (amino acids 431 to 649 of HPV16 E1 and 438 to 657 of HPV18 E1), or the entire regions (amino acids 1 to 649 of HPV16 E1 and 1 to 657 of HPV18 E1) between HPV16/18 E1s are presented.