HCMV is capable of infecting an extensive range of cell types in vivo. According to Compton (2004), the infection of a fibroblast begins with an initial tethering of a virion to cell surface - heparan sulfate proteoglycans. Then the HCMV glycoprotein, gB, is directly fused to cellular receptors such as epidermal growth factor receptor (EGFR) and cellular integrins occurs at neutral pH (Compton, 1992). The fusion with the envelope is followed by attachment of the virion and release into the cytoplasm (Roizman & Pellet, 2001). HCMV entry into epithelial and endothelial cells occurs through endocytosis in a low-pH condition (Ryckman et al., 2006) using the viral glycoproteins UL131-128 (Hahn et al., 2004). Infected cells show several…show more content… In HCMV, there are four forms of capsids which are pre-B, B, C and A (Wood et al., 1996).
The development of capsids begins with the movement of capsid proteins from the site of synthesis in the cytoplasm to the nucleus where the capsid will be assembled (Gibson, 1996). The capsid shell proteins consist of major capsid protein (MCP), minor capsid protein (mCP), mCP binding protein (mC-BP), and the smallest capsid protein (SCP) (Gibson, 1996). Most of the capsid proteins are small enough to diffuse through the nuclear pores. However, the major capsid protein must merge with the assembly protein precursor (pAP) that directs the transport of the MCP/pAP complex through the nuclear pore (Figure 1.2) (Wood et al., 1996). The four shell proteins, MCP, mCP, mC-BP, and SCP, and two precursor internal proteins merge to form a pre-B capsid. The two internal proteins are cleaved developing a B capsid which contain internal scaffolding proteins (Wood et al., 1996). A capsid developed as a result of failed DNA packaging. They contain all of the structural components as a B capsid but lack the assembly protein and are considerably larger than B capsids (Gibson, 1996).
Maturation of HCMV involves the packing of B capsids with viral DNA resulting in the formation of mature C capsids. The C capsid is encompassed of the viral DNA genome and a shell with tegument proteins (Gibson, 1996). In the maturation process, the nuclear lamina is