FIG. 2.

Phage L Dec protein binds to P22 virions. The indicated proteins were separated by 12.5% polyacrylamide-SDS gel electrophoresis and stained with Coomassie brilliant blue R-250. Phage L N-terminally histidine-tagged Dec protein (lane Dec-HisN) was purified as described in Materials and Methods. Purified P22 virions (lane P22) were mixed with this Dec protein (25.0 μg of Dec per μg [10¹⁰] of virions) and incubated at room temperature for 30 min in 1 mM MgCl₂-10 mM TrisCl (pH = 7.4) (TM). The mixture was then sedimented onto a CsCl (density = 1.6 g/cc) cushion, and the virion-sized material was dialyzed against 1 mM MgCl₂-10 mM TrisCl (pH = 7.4) (lane P22+Dec-HisN); a parallel experiment with multiple rounds of CsCl purification or with more than 10 times as much Dec protein showed an identically intense Dec band relative to coat protein (data not shown), showing that the particles used for the figure were saturated with Dec protein. Identical results were obtained in a similar experiment with C-terminally histidine-tagged Dec. Purified L virions are shown in lane L for comparison. The oligonucleotide-histidine tag retards the Dec protein's migration somewhat in SDS-polyacrylamide electrophoresis gels. P22 gp1 is portal protein (gp nomenclature refers to the fact that this is the gene product of gene 1); gp16 is an injection protein; gp5 is coat protein.