TOPOGRAPHICAL STUDIES OF BACTERIOPHAGE-PHI-29 CONNECTOR BIDIMENSIONALCRYSTALS USING SCANNING-TUNNELING-MICROSCOPY

Reversed metal replicas of the bacteriophage Phi 29 connector bidimens ional crystals were observed with the scanning tunneling microscope (S TM). This technique can complement structural information obtained fro m transmission electron microscopy by providing direct height measurem ents of the structures. The STM images revealed information about the surface topography of the crystals. Individual connectors can be easil y distinguished. It is confirmed that neighboring connectors have oppo site orientations with respect to the substrate, as has been described previously (Carazo et nl., 1986, J. Mel. Biol, 192, 853-867) and we m easure that the smaller domain protrudes 1.3 +/- 0.2 nm from the wide domain of the neighboring connectors. An overall view of the crystal s urface reveals areas where loose protein has deposited and ordered reg ions of different thicknesses. These areas can have two different heig hts with respect to the first layer of the bidimensional crystal: (a) 7.0 +/- 0.5 nm, compatible with the the presence of two overlapping la yers of proteins and (b) 4.0 +/- 0.5 nm, compatible with regions origi nated by a change in the orientation of neighboring connectors. Copyri ght (C) 1996 Elsevier Science Ltd