In this task, you are given a passage which has a question and the context. You have to generate an answer to the question based on the information present in the context.

[EX Q]: Context: To investigate the existence condition of hepatitis B surface antigen(HBsAg) termination codon bias.', 'A total of 174 reference sequences of all kinds of Hepatitis B virus(HBV) genotypes were chosen from GenBank, and compared by BioEdit. Then secondary structure of RNA was constructed and analyzed together.', '(1) There were two types of HBsAg termination codon: TAA and TGA in 174 reference sequences. TAA was in 124 cases (71.26%); and TGA in 50 cases (28.74%). (2) There was codon bias selection in HBsAg termination codon, and it could affect the secondary structure of RNA and amino acid sequence encoding protein.\Question: Does [ Hepatitis B surface antigen terminate codon bias selection ]?
[EX A]: HBsAg termination codon bias exists and may be related to RNA structure and the conservation of protein function in the evolutionary progress.

[EX Q]: Context: Dipeptidyl peptidase-4 (DPP4) was recently proposed as a novel adipokine linked to insulin resistance (IR). As IR represents a cluster of disorders in hepatic and muscle cell insulin signalisation, we aimed to assess the possible correlation between fasting serum DPP4 activity, IR and liver enzymes in order to elucidate the question of hepatic contribution to serum DPP4 activity.', 'This cross-sectional study comprised 44 T1DM patients aged 18 to 65years. IR was estimated using the equation derived from euglycemic-hyperinsulinemic clamp studies-estimated glucose disposal rate (eGDR). DPP4 serum activity was determined spectrophotometrically as a rate of cleavage of 7-amino-4-methyl coumarin (AMC) from H-Gly-Pro-AMC. The patients were divided into two groups according to the mean value of fasting serum DPP4 activity (31.42U/L).', 'The group with lower fasting serum DPP4 activity had lower mean rate of liver biomarkers alanine aminotransferase (ALT) (p=0.001) and aspartate aminotransferase (AST) (p=0.002) while higher eGDR (p=0.003) compared to group with higher DPP4 activity. DPP4 activity showed positive correlation with AST (r=0.358, p=0.017) and ALT (r=0.364, p=0.015) while negative correlation with eGDR (r=-0.612, p<0.001). ALT remained positively associated with fasting serum DPP4 activity after controlling for age, gender, diabetes duration, the use of statins and antihypertensives (p=0.025).\Question: Is fasting serum dipeptidyl peptidase-4 activity independently associated with alanine aminotransferase in type 1 diabetic patients?
[EX A]: Fasting serum DPP4 activity might be associated with hepatic IR in T1DM patients and a part of soluble DPP4 activity might be of a hepatic origin. Further study investigation is warranted to elucidate this topic.

[EX Q]: Context: Nonviral vectors based on polyethylenimine (PEI) usually contain an excess of PEI that is not complexed to DNA. Since unbound PEI contributes to cellular and systemic toxicity, purification of polyplexes from unbound PEI is desirable.', 'Size exclusion chromatography (SEC) was used to purify PEI polyplexes of free PEI. Transfection properties of purified polyplexes and the effect of free PEI on gene delivery were studied in vitro and in vivo after systemic application into mice.', 'SEC did not change the size and zeta-potential of polyplexes. Independent of the amount of PEI used for complex formation, purified PEI polyplexes had the same final PEI nitrogen/DNA phosphate ratio of 2.5. Notably, purified PEI polyplexes demonstrated low cellular and systemic toxicity. High transfection efficiency was achieved with purified polyplexes at high DNA concentrations (8-15 microg/ml). At low DNA concentrations (2-4 microg/ml) gene transfer with purified particles was less efficient than with polyplexes containing free PEI both in vitro and in vivo. Mechanistic studies showed that free PEI partly blocked cellular association of DNA complexes but was essential for the following intracellular gene delivery. Adding free PEI to cells treated with purified particles with a delay of up to 4 h resulted in significantly enhanced transfection efficiency compared with non-purified particles or purified particles without free PEI.\Question: Does purification of polyethylenimine polyplexes highlight the role of free polycations in gene transfer?
[EX A]:
This study presents an efficient method to remove free PEI from PEI polyplexes by SEC. Our results from transfection experiments demonstrate that free PEI substantially contributes to efficient gene expression but also mediates toxic effects in a dose-dependent manner. Purified polyplexes without free PEI have to be applied at increased concentrations to achieve high transfection levels, but exhibit a greatly improved toxicity profile.