LIFE SCIENCE

Detailed explanation-1: -The many proteins that function in the nucleus-including histones, DNA and RNA polymerases, gene regulatory proteins, and RNA-processing proteins-are selectively imported into the nuclear compartment from the cytosol, where they are made.

Detailed explanation-2: -The GTPase Ran regulates the interaction between receptors and cargoes, or adapters, and is crucial in providing directionality to nuclear import and export.

Detailed explanation-3: -One the best characterised is the NLS of the hnRNP A1 protein. This NLS, designated M9, is constituted by 38 aminoacids. Surprisingly, this sequence was found to be essential for both the nuclear import and export of the protein [33].

Detailed explanation-4: -Nuclear import Proteins, transfer RNA, and assembled ribosomal subunits are exported from the nucleus due to association with exportins, which bind signaling sequences called nuclear export signals (NES).