STRUCTURE AND THERMODYNAMICS OF NONALTERNATING C/G BASE PAIRS IN Z-DNA: THE 1.3 ANGSTROMS CRYSTAL STRUCTURE OF THE ASYMMETRIC HEXANUCLEOTIDE D(M(5)CGGGM(5) CG)/D(M(5) CGCCM(5)CG) DNA, Z-DNA, DOUBLE HELIX, MODIFIED 145D