Inrecent years therehasbeen atremendousincreaseinour understandingofthe functioningofthe cellat the molecular leveL This has been achieved in the main by the invention and developmentof new methodology, particularlyin that area generally referred to as "genetic engineering. " Al- though this revolution has been taking place in the field of nucleic acids research, the protein chemist has at the same timedevelopedfresh methodologytokeeppace with the re- quirements ofpresent-daymolecularbiology. Today's mo- lecularbiologistscannolongerbecontentwithbeingexperts inoneparticulararea alone. Theyneedtobeequallycompe- tentin the laboratory at handling DNA, RNA, and proteins movingfrom one area toanotherasrequiredby theproblem thatisbeing solved. Althoughmanyof thenewtechniques in molecularbiologyare relativelyeasy tomaster, itisoften difficult for a researcher to obtain all the relevant informa- tionnecessaryforsettingupandsuccessfullyapplyinganew technique. Informationisofcourse availablein the research literature, but this often lacks the depth of description that the new user requires. This requirement for in-depth prac- tical details has become apparent by the considerable de- mand for places on our Molecular BiologyWorkshops held at Hatfield each summer. Volume 1of this series describedpracticalprocedures for a range of protein techniques frequently used by research workers in the field of molecular biology. Because of the limitations on length necessarily inherent in producing any v vi Preface book, one obviouslyhad to be selective in the choiceof titles forVolume1. TheproductionofVolume 3, therefore, allows the development of the theme initiated in Volume 1. This volumecontains afurther selection ofdetailed protocols for arangeofanalyticalandpreparativeproteintechniques, and should be seen as a continuation of Volume 1. Companion Volumes2and4provideprotocols fornucleic acid method- ology. Each methodisdescribedby an authorwhohas regularly used the technique in his or her ownlaboratory.