Santa's Little Helper reason he stopped performing as Santa's Little Helper was because "The producers thought... 'Hmmm, Dan barks pretty good, and we are already paying him and he seems to like doing the dog thing... why do we need to pay Welker who comes in here, spends less than an hour, eats all the doughnuts, refuses to come to rehearsals... let's just give the damn dog to Dan!'" Santa's Little Helper has become a well-known dog because of his appearances in the series. A writer for "The Grand Rapids Press" wrote in 2002 that "we all know who Homer, Marge, Bart, Lisa
Helper dependent virus and capsid encoding DNA, plus helper DNA. Every cell that is successfully transfected with all three DNA fragments will produce the necessary proteins to produce infective viruses. These viruses will only have transgenic DNA encapsidated and therefore once they've infected a patient's cell, they will not be capable of reproducing. Helper dependent viruses can also occur in nature without being "gutted". The term satellite virus has been given to a large group of viruses that all require the presence of another virus to replicate. Many of these are plant viruses, but animal viruses can be seen in the case of