What is the fine-grained topic of the following text: The m7G-cap is converted to m3G-cap, which is a hypermethylated structure of 5&rsquo;-end, by cytoplasmic catalytic protein TSG1 and the m3G-capped U snRNA forms snRNP with Sm proteins in the cytoplasm, followed by entry into the nucleus. Only return the topic.
Conversion of m7G-cap to m3G-cap by TSG1 protein and formation of snRNP in the cytoplasm