The head shell is bound by the D protein which stabilizes the coat protein shell. However, if Nu1, A, or FI are missing, DNA is not packaged and as a consequence, the coat shell does not expand, and D can only add after expansion. We could confirm the A-Nu1 interaction as well as the interactions between FI and A and FI and E which were previously known only from genetic experiments

[21, 22]. We also confirmed the D-E and E-E interactions. The terminase and the portal CB-839 concentration proteins are the largest proteins of the lambda head. Using fragments of these proteins as baits – as opposed to full-length proteins – may result in additional Stattic ic50 interactions, especially since we were not able to detect most of the B interactions reported in the literature (Tables 2 and 4). Tail assembly and structure Tail assembly is even less well understood than head assembly (Figure 6). From genetic analyses it is known that the host receptor protein J initiates the process with I, L, K, and G (including its fusion protein G-T) successively joining the process [23]. Older studies suggest a slightly different

order of action, namely J > I > K > L [24]. In fact, it is not known if I, L and M are components of the finished selleck screening library virion or are assembly factors that are not present in virions. It is thus difficult to reconstruct the detailed molecular events during tail assembly. In any case, J eventually associates with the tape measure protein H, and the major tail protein V forms a tube around this central rod. U finally joins the head-proximal part of the tail. Similarly, W and FII join to the portal protein in the head

to form the binding site for the tail. The main tail proteins are connected by known direct protein-protein interactions (Table 2) but the interactions during the initiation of tail assembly have eluded previous studies. In fact, we failed to detect any interaction involving J and I, and the only interactions of L and K did not involve other tail proteins (Table 4). However, we did find several new interactions that are potentially relevant for tail assembly. For instance, G, a fairly promiscous protein with a total PIK-5 of 8 interactions, was found to bind to V, G, T, H, and M. It is thus possible that it acts as a scaffold organizing the assembly of the tail. By contrast, the interactions of H and V with G were their sole tail-related interactions. We did not find the tail fiber proteins Stf and Tfa to interact with other tail proteins in our screens. Stf has been speculated to assume a trimeric structure, similar to the tail fiber protein of phage T4 [25] although there is no specific evidence for oligomerization in lambda. Figure 6 Tail assembly. The lambda tail is made of at least 6 proteins (U, V, J, H, Tfa, Stf) with another 7 required for assembly (I, M, L, K, G/T, Z). Assembly starts with protein J, which then, in a poorly characterized fashion, recruits proteins I, L, K, and G/T to add the tape measure protein H.