TASK DEFINITION: In this task, you are given a sentence from the research paper and your task is to classify the given sentence into the following categories: Background (Why is this problem important? What relevant works have been created before? What is still missing in the previous works? What are the high-level research questions? How might this help other research or researchers?), Purpose (What specific things do the researchers want to do? What specific knowledge do the researchers want to gain? What specific hypothesis do the researchers want to test?), Method (How did the researchers do the work or find what they sought? What are the procedures and steps of the research?), or Finding (What did the researchers find out? Did the proposed methods work? Did the thing behave as the researchers expected?). 
PROBLEM: which is characterized by elevated GFAP expression in astrocytes.

SOLUTION: background

PROBLEM: Expression of a small ( 35aa ) sequence in Domain III alone was sufficient to form speckles for all 3 viral nsp15s.

SOLUTION: finding

PROBLEM: Then , the recombinant fragment in pMD18-T was subcloned into corresponding sites of prokaryotic expression vector pGEX-6P-1 after digestion with EcoRI and XhoI to construct a recombinant fusion expression vector pGEX-6P-M.

SOLUTION:
method