Core Concept: What is SELEX? SELEX (Systematic Evolution of Ligands by EXponential Enrichment) is an iterative, in vitro selection process. It starts with a vast, random library of oligonucleotides (10^14 - 10^15 unique sequences) and, over multiple rounds, enriches for those that bind to the target. Standard Multi-Round SELEX Screening Service Workflow A full-service provider will typically manage the entire process, which can be broken down into key phases: Phase 1: Project Design & Target Preparation Target Consultation: Defining the target (e.g., protein, small molecule, cell, virus). Critical discussion of target purity, immobilization strategy, and selection conditions (buffer, temperature, counter-selection). Library Design: Selection of a random library (e.g., 40-nt random core with fixed primer sites). Options include DNA, RNA (requiring reverse transcription), or modified libraries (e.g., with 2'-F pyrimidines for nuclease resistance). Immobilization Strategy: The service provider will choose the best method: Immobilized Target: (Most common for proteins) Binding target to beads (streptavidin, Ni-NTA for His-tag) or columns. Counter-Selection: Using negative control surfaces (e.g., blank beads, related but undesired proteins) to subtract non-specific binders. Phase 2: The SELEX Cycle (Repeated 8-15 Rounds) This is the core iterative screening process. Each round consists of: Incubation: The oligonucleotide library is incubated with the target under defined conditions. Partitioning: Separation of…
