Retroviruses, Tumor Viruses and Viral Proteins

**3**

**Chapter 1**

**Abstract**

favoring biochemical reactions.

Multiple Functions and

Nucleocapsid Proteins of

*Jean Luc Darlix and Hugues de Rocquigny*

Retroviruses and Hepadnaviruses

This chapter aims at presenting small viral proteins that orchestrate replication of the human immunodeficiency virus type-1 (HIV-1) and the human hepatitis virus (HBV), two canonical examples of small human pathogens. HIV-1 nucleocapsid protein (NC) and the C-terminal domain (CTD) of the HBV core protein (HBc) are essential structural components of the virus capsid ensuring protection of the viral genome; they also chaperone replication of the HIV-1 genomic RNA and the HBV DNA by a reverse-transcription mode, and later, these proteins kick-start virus morphogenesis. HIV-1 NC and HBV CTD belong to the family of intrinsically disordered proteins (IDP), a characteristic rendering possible a large number of molecular interactions. Although these viral proteins share little sequence homologies, they have in common to be rich in basic amino acids and endowed with RNA-binding and chaperoning activities. Similar viral RNA-binding proteins (vRBP) are also encoded for by other virus families, notably flaviviruses, hantaviruses, and coronaviruses. We discuss how these vRBPs function based on the abundant RBP family that plays key physiological roles via multiple interactions with non-coding RNA regulating immune defenses and cell stress. Moreover, these RBPs are flexible molecules allowing dynamic interactions with many RNA and protein partners in a semi-solid milieu

**Keywords:** RBP, HIV, HBV, IDP, RNA chaperoning, molecular crowding

Viruses that replicate their genome by the process of reverse transcription (RTion) are common in animals, plants, algae, and fungi [1]. These so-called reverse-transcribing viruses have been classified into five different families, namely, *Caulimoviridae*, *Hepadnaviridae*, *Metaviridae*, *Pseudoviridae*, and *Retroviridae* to which was the recently added *Belpaoviridae* [2]. Among these widespread viruses, two are major human pathogens, the human immunodeficiency virus type 1 (HIV-1)

Retroviruses exist as infectious exogenous RNA viruses as well as endogenous retroelements (ERV) present at high copy numbers in the genome of vertebrates.

**1. Forewords on viruses and RNA chaperones**

and the human hepatitis B virus (HBV).

Disordered Nature of
