This is a fundamental question about basic phage library construction. I know that people can construct library by either phage vector (eg. M13KE) or phagemid+helperphage. Based on my understanding, phage vector has everything we need to assemble a phage and we insert our library pieces into the vector; xhagemid is a plasmid only express pIII protein with library pieces; and helperphage contains everything on wild type phage. So why we cannot use a blank M13KE vector as a helperphage? and if we only need a pIII protein source, can M13KE with library pieces insertion serve the same function as phagemid and produce monovalent library by adding additional helper phage?
thank you
In theory you can use any plaque forming M13 variant as the helper phage for a phagemid, however the standard helper phages that are generally used carry a mutation that reduces their packaging proficiency so that phagemid vectors are preferentially packaged, otherwise wild type helper phage would outcompete.
Generally you can use phage vectors for small insertions that are "In-frame" so that pIII is preserved and expressed. With larger inserts it is often easier to just use a phagemid plus helper. But there are certainly situations where you could use either.
Yes, longer protein atttached to gpIII will have a much higher probability of disrupting the protein's ability to translocate and be assembled into the phage tail.
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