5 CGCCGTCATG-3 Label 5'end with 32p 5 32P-CGCCGTCATG3 Cleave Cleave Cleave Cleave atG's atA's&G's atC's&Ts at C's Direction of electrophoresis 3 P-CGCCGTCATG 10 G 9 T A 7 6 T 32P-CGCCG 5 4 c 3 sp -cG} 2 G 1 c Autoradiogram Fragment Deduced length sequence in bases Figure 3-48 The Maxam-Gilbert Chemical Cleavage Method for Sequencing DNA In tbis procedure.four different cbemi cal reagents are employed to cleave single-stranded DNA cbains adjacent to particular bases.The radiouctive fragments are tben separated on the basis of size by gel electropboresis (page 145).wbicb allous the sequential arrangement of bases in the original DNA molecule to be determined.The autoradiogram on the left shows ubat such gels look like.The diagram illus trates the banding pattern that would be observed for a DNA molecule wbose sequence is CGCCGTCATG read in the 53 direction.To belp sbow ubat sucb gel patterns mean,the sequences of tbe tbree fragments produced by the reagent that cleaves adjacent to G residues are provided at the left of tbe diagram.6/92 6/95