▁than ▁the ▁database , ▁e . g ., ▁the ▁query ▁may ▁be ▁one ▁thousand ▁nucle ot ides ▁while ▁the ▁database ▁is ▁several ▁billion ▁nucle ot ides . ▁ ▁The ▁main ▁idea ▁of ▁B LA ST ▁is ▁that ▁there ▁are ▁often ▁High - sc oring ▁Seg ment ▁P airs ▁( H SP ) ▁contained ▁in ▁a ▁statist ically ▁significant ▁alignment . ▁B LA ST ▁searches ▁for ▁high ▁scoring ▁sequence ▁align ments ▁between ▁the ▁query ▁sequence ▁and ▁ ▁the ▁existing ▁sequences ▁in ▁the ▁database ▁using ▁a ▁he ur istic ▁approach ▁that ▁approxim ates ▁the ▁Smith - W at erman ▁algorithm . ▁However , ▁the ▁exhaust ive ▁Smith - W at erman ▁approach ▁is ▁too ▁slow ▁for ▁searching ▁large ▁genom ic ▁databases ▁such ▁as ▁Gen B ank . ▁Therefore , ▁the ▁B LA ST ▁algorithm ▁uses ▁a ▁he ur istic ▁approach ▁that ▁is ▁less ▁accurate ▁than ▁the ▁Smith - W at erman ▁algorithm ▁but ▁over ▁ 5 0 ▁times ▁faster . ▁[ 8 ] ▁The ▁speed ▁and ▁relatively ▁good ▁accuracy ▁of ▁B LA ST ▁are ▁among ▁the ▁key ▁technical ▁innov ations ▁of ▁the ▁B LA ST ▁programs . ▁ ▁An ▁over view ▁of ▁the ▁B LA ST ▁algorithm ▁( a ▁protein ▁to ▁protein ▁search ) ▁is ▁as ▁follows : ▁▁ ▁Remove ▁low - complex ity ▁region ▁or ▁sequence ▁repe ats ▁in ▁the ▁query ▁sequence . ▁ ▁" L ow - complex ity ▁region " ▁means ▁a ▁region ▁of ▁a ▁sequence ▁composed ▁of ▁few ▁kinds ▁of ▁elements . ▁These ▁regions ▁might ▁give ▁high ▁scores ▁that ▁conf use