TWR CTLR INTERVENED AND STOPPED FLC OF AN SMT TURBOPROP AFTER THEY HAD CROSSED A RWY HOLD SHORT LINE DURING TAXI OUT FOR TKOF.

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WE RECEIVED TAXI CLRNC TO RWY 4L AT BOS AND TOLD TO GIVE WAY TO 2 B727'S; THEN TAXI VIA TXWYS B AND E. WE TAXIED OFF THE GA RAMP AND MADE A WRONG TURN ON TXWY B AND STARTED TO TAXI ACROSS THE TXWY B HOLD SHORT LINES ONTO THE RWY 27 STOP WAY. THE GND CTLR TOLD US TO STOP AND MAKE A 180 DEG TURN AND THAT WE ALMOST CROSSED THE ACTIVE RWY. WE MADE THE 180 DEG TURN AND TAXIED BACK PAST THE HOLD POINT TO GET OUR BEARINGS. WE REALIZED WHERE WE WERE AND FINISHED OUR TAXIING TO THE RWY. SEVERAL FACTORS CONTRIBUTE TO THIS OCCURRENCE; ONE WHICH WAS THE FACT THAT THIS WAS OUR FIFTH LEG AFTER BEGINNING THE DAY AT XX00; SO WE WERE BOTH TIRED AND WANTED TO FINISH THE DAY. SECONDLY; WE WERE ASSUMING WE WERE TO FOLLOW ONE OF THE B727'S THAT WAS TAXIING OUT TO RWY 4R WHICH WAS WRONG. SOME OTHER CONSIDERATIONS MAY HAVE BEEN OUR LACK OF CREW COORD; AS I RELIED ON MY COPLT TO DIRECT ME; WITHOUT MY HAVING THE PICTURE OF THE TAXI RTE IN MY MIND. I NOW REALIZE THAT THE IDEA OF A 2 PLT CREW IS NOT NECESSARILY TO RELY SOLELY ON THAT PERSON; MORE SO TO CONFIRM THINGS WITH ONE ANOTHER; ESPECIALLY TAXI ROUTINGS IN COMPLEX ARPT ENVIRONMENTS. THE ONLY TFC WAS ON A SEVERAL MI FINAL AND TO MY KNOWLEDGE THEY WERE NOT AWARE OF THE SIT.