The FI gene product of bacterial virus Lambda is related to the E. coli chromosomal protein NS2 and is involved in intracellular DNA organization.

A likely function of the Lambda FI gene product (gpFI) is condensation of developmental forms of the bacteriophage DNA in the host cell. Several characteristics of gpFI support this hypothesis: it is similar in its structure and properties to E. coli NS proteins whose involvement in the bacterial DNA condensation has been established and it comigrates with DNA during fractionation of host cell lysate through a sucrose gradient.