Because of the high cost of the technique and complexity of the computational analysis. Moreover, because only a single MDR patient was longitudinally analyzed, the results obtained regarding changes in the viral quasispecies under the effect of antiviral treatments require corroboration by Lomitapide Mesylate further studies Benzethonium Chloride examining additional patients. In addition, due to the 250-bp-length limitation of the standard GS-FLX chemistry, the relevant NA-resistant substitutions, rtI233V and rtN236T linked to ADV treatment failure, and rtM250I/V linked to ETV failure, located outside the B and C HBV RT functional domains, were excluded from the fragment analyzed. However, this last limitation was not considered relevant because we only selected patients who did not show NA resistant substitutions outside the region analyzed, as assessed by LiPA and/ or direct sequencing during follow-up. To summarize, UDPS detected minor variants comprising less than 0.1% of the HBV viral quasispecies. Nonetheless, the information provided did not enable prediction of which resistant aa substitutions would be selected during treatment. Additional studies are needed to determine at what frequency HBV variants become clinically relevant. However, the high sensitivity of this technology has resulted in some unexpected findings: first, the high degree of conservation of residue rtL155 and a significant percentage of defective genomes at baseline that became the predominant population after LMV and ADV treatments. These results suggest that the HBV quasispecies has an active trans-complementation mechanism enabled by coinfection of cells with multiple variants. Second, as tested in one sequentially treated patient, assessing and ranking the variability of aa substitutions through sequential treatment using a “blinded” algorithmic method driven by an objective variability measure of their frequencies highlighted the most important substitutions occurring during this period, with no need for previous knowledge about HBV variants and their resistance to antiviral treatments. Therefore, this method can potentially act as a “scanning tool” to detect new resistant variants in viral quasispecies, and indicates a role as a “phenotype-like” method that provides information on the relative susceptibility of these variants to any type of selective pressure. Quantitative UDPS analysis was also useful to analyze the global variability of the HBV quasispecies and its evolution, by quantifying the nt and aa divergences of its sequences. Lastly, the partial picture of reality provided by UDPS analysis of individual substitutions is significantly improved 
by linkage analysis, which allows detection and quantification of variant combinations, which seem to be the most common cause of resistance in anti-HBV therapy in our sequentially treated patient. In conclusion, UDPS offers significant advantages for the study of viral quasispecies, although currently its potential is mainly limited by its high cost. As new applications for this technology are developed, it is likely that the cost will significantly decrease. The level of membrane proteins at the plasma membrane is regulated by post-translational modifications including phosphorylation and ubiquitination. For example, Epithelial Growth Factor Receptor is ubiquitinated and internalized leading to the recycling of EGFR and/or the degradation of both receptor and its ligand. In addition, both tyrosine and non-tyrosine kinase receptors are ubiquitinated and degraded in a proteasome-dependent manner.