The strains of respiroviruses, avulaviruses, and the majority of rubulaviruses, that have HN in their envelopes, use sialic acids as their cell entry receptors. SeV, as a representative of respiroviruses, uses molecules containing sialic acids residues such as glycoproteins and gangliosides. SeV also can use lectins for a cell entry. Three SeV receptors are represented by molecules that are clusters of differentiation. The structures of some of these receptors are available for visualization through SugarBindDB - a resource of glycan-mediated host–pathogen interactions. Others are available through KEGG Glycan Database, PubChem compound database, and TOXNET database (toxicology data network) of US National Library of Medicine. Because SeV is a negative-strand RNA virus the virus entire life cycle is completed in the cytoplasm using its own RNA polymerase. Sendai virus initiates infection process by host cell adsorbtion mediated by the recognition of specific receptor molecules. Hemagglutinin neuraminidase (HN) serves as a virus cell attachment protein that interacts with a specific cell entry receptor. NH has sialidase activity, and it is capable of cleaving sialic acid residues from the cell receptor. This cleavage triggers the fusion process of viral envelope and cell membrane, which promotes by cooperation of NH with the viral fusion protein (F). To perform the fusion function F protein must be proteolytically activated from it precursor inactive form F0. This activation requires F0 cleavage by host protease before the virus adsorbtion (see the section “proteolytic cleavage by cellular proteases”). After a merging of the host membrane and the viral envelope, the SeV according to one model is “uncoating” with diffusion of the viral envelope proteins into the host plasma membrane. According to another model the virus did not release its envelope proteins into the host membrane. The viral and host membranes are fused and a connecting structure is made. This connecting structure serves as a transportation "highway" for the viral ribonucleoprotein (RNP). Thus, RNP travels through the connecting structure to reach the cell interior allowing SeV genetic material to enter the host cell cytoplasm. Once in the cytoplasm, the SeV genomic RNA is getting involved, as a template, in two different RNA synthetic processes performed by RNA-dependent RNA polymerase, which consists of L and P proteins: (1) transcription to generate mRNAs and (2) replication to produce a positive-sense antigenome RNA that in turn acts as a template for production of progeny negative-strand genomes.