Eukaryotic Cell Organelles

Eukaryotic cells are quite distinct containing nuclear and cytoplasmic compartments. The nucleus is a membrane-enclosed organelle that is surrounded by a nuclear envelope (NE). In the cells a lot of transportation occurs. One of the reasons is that nuclear proteins are synthesised in the cytoplasm, but are needed in the nucleus. Another reason is that to be able to synthesize the proteins that are required for the cell, the different RNA species located in the nucleus are needed in the cytoplasm (6).

The nucleus is only able to import and export molecules through signal-dependent transport and through passive diffusion via nuclear pore complexes (NPCs) that are situated on the nuclear envelope. An aqueous channel is created by each NPC that

It has three layers that are composed of the fibrillar center (FC), the dense fibrillar component (DFC) and the granular component (GC). The nucleolus is a non-membrane bound organelle and found in the nucleoplasm. Though it lacks a membrane, one cannot assume that the diffusion rate to each layer is equal. Its function is to transcribe rDNA, remove introns from pre-rRNA and modify an rRNA with the assistance of ribosomal proteins. The modifications made on the rRNA are executed by small nuclear ribonucleoprotein (snRNP) complexes which consist of small nucleolar RNAs (snoRNAs) and nucleolar proteins. The snoRNAs are part of the splicing but they are also responsible for the structure of the mature rRNA

Retroviruses have the ability to replicate in host cells by reverse transcription. HIV consists of 6 novel genes and 3 common genes for all retroviruses. The gene of interest is rev which encodes a 116-amino acid regulatory protein; HIV-1 Rev protein. Its function is to regulate HIV-1 structural protein expression, typically gag and env proteins. The Rev protein is found in the nuclei of infected cells, though it interacts mostly with the nucleoli (16, 17).

The Rev protein regulates the export of unspliced and partially spliced HIV-1 RNA species. This is achieved by binding to the Rev Response Element (RRE) on the unspliced mRNA species and transports it out to the cytoplasm. However, the RNA-Rev protein complex uses a different nuclear export pathway than the fully spliced mRNA. The spliced versions of the HIV-1 mRNA species do not contain the RRE, and are therefore not dependent of the Rev protein (18,