aps ▁or ▁alignment ▁characters ▁( see ▁sequence ▁alignment ). ▁Se qu ences ▁are ▁expected ▁to ▁be ▁represented ▁in ▁the ▁standard ▁I UB / I UP AC ▁am ino ▁acid ▁and ▁nucle ic ▁acid ▁codes , ▁with ▁these ▁exceptions : ▁lower - case ▁letters ▁are ▁accepted ▁and ▁are ▁mapped ▁into ▁upper - case ; ▁a ▁single ▁hy phen ▁or ▁dash ▁can ▁be ▁used ▁to ▁represent ▁a ▁gap ▁character ; ▁and ▁in ▁am ino ▁acid ▁sequences , ▁U ▁and ▁* ▁are ▁acceptable ▁letters ▁( see ▁below ). ▁N umer ical ▁digits ▁are ▁not ▁allowed ▁but ▁are ▁used ▁in ▁some ▁databases ▁to ▁indicate ▁the ▁position ▁in ▁the ▁sequence . ▁The ▁nucle ic ▁acid ▁codes ▁supported ▁are : ▁ ▁The ▁am ino ▁acid ▁codes ▁supported ▁( 2 2 ▁am ino ▁ac ids ▁and ▁ 3 ▁special ▁codes ) ▁are : ▁ ▁FA ST A ▁file ▁ ▁Fil ename ▁extension ▁There ▁is ▁no ▁standard ▁filename ▁extension ▁for ▁a ▁text ▁file ▁containing ▁FA ST A ▁formatted ▁sequences . ▁The ▁table ▁below ▁shows ▁each ▁extension ▁and ▁its ▁respective ▁meaning . ▁ ▁Com pression ▁The ▁compression ▁of ▁FA ST A ▁files ▁requires ▁a ▁specific ▁compress or ▁to ▁handle ▁both ▁channels ▁of ▁information : ▁ident ifiers ▁and ▁sequence . ▁For ▁improved ▁compression ▁results , ▁these ▁are ▁mainly ▁divided ▁in ▁two ▁streams ▁where ▁the ▁compression ▁is ▁made ▁assuming ▁independence . ▁For ▁example , ▁the ▁algorithm ▁M F Com press ▁ ▁performs ▁loss less ▁compression ▁of ▁these ▁files ▁using ▁context ▁mod elling ▁and ▁arithmetic ▁encoding . ▁For ▁a ▁benchmark ▁on ▁FA ST A ▁files