THE LEADZYME RIBOZYME BOUND TO MG(H2O)6(II) AND SR(II) AT 1.8 A RESOLUTION 1NUV RNA, RIBOZYME, LEADZYME, LEAD-DEPENDENT CLEAVAGE, MG(H2O) 6(II), BULGED NUCLEOTIDES, HYDRATED MAGNESIUM, SR(II), PSEUDOHELICAL PACKING, STICKY ENDS, ALTERNATE CONFORMATION, HOMOPURINE BASE PAIRS