An investigator identified a C-terminal nuclear localization signal (NLS; Pro-Lys-Lys-Lys-Arg-Lys) on Protein X (50 kDa). Fusion of GFP at the C-terminus of Protein X (X-GFP) resulted in cytosolic localization. However, when the NLS was fused to the N-terminus of GFP (NLS-GFP), it localized extensively to the nucleus. The investigator proposed the following hypotheses: A. The basic amino-acid stretch of the NLS in the X-GFP chimeric construct is sterically masked by the GFP sequence. B. Protein X in the full-length X-GFP chimeric protein undergoes post-translational modifications that inhibit nuclear import. C. Fusion with GFP makes Protein X too bulky to physically pass through the nuclear pore complex. D. GFP is post-translationally modified in a way that actively blocks the import of the X-GFP protein. Which one of the following options represents the combination of all plausible hypotheses?

Arrange the following events in the correct chronological order during receptor-mediated endocytosis of LDL and its subsequent intracellular fate: A. LDL binds to the LDL receptor in a clathrin-coated pit at the plasma membrane B. Dynamin oligomerises at the neck of the coated pit and hydrolyses GTP to pinch off the vesicle C. Clathrin triskelions are recruited via AP-2 adaptor binding to the NPXY internalisation signal of the LDL receptor D. Acidification of the early endosome (pH ~6) causes dissociation of LDL from its receptor E. LDL receptor is recycled to the plasma membrane via Rab11-positive recycling endosomes F. Cholesterol esters are hydrolysed by lysosomal acid lipase after late endosome–lysosome fusion

A researcher treats cultured mammalian cells with Brefeldin A (BFA) for 30 minutes and then labels newly synthesised proteins with 35S-methionine. She finds that: - Labelled proteins accumulate in the ER. - The cis-Golgi marker GM130 redistributes to the ER. - Lysosomal enzyme precursors (bearing mannose-6-phosphate) are secreted into the medium instead of reaching lysosomes. Which of the following mechanistic statements best explains all three observations?