passages.id: split_4_test_970_passage
passages.type: progene_text
passages.text: Based on this , a novel plasmid vector was conceived , named pTREX - n , which retains the neo gene of pRIBOTEX as a positive selectable marker and replaces the CAT - SV40 cassette in pRHX1CAT40 by a multiple cloning site .