Protein P is synthesized in relatively high amounts in the human pancreas. This protein has been isolated and purified, but its amino acid sequence has not been determined. We wish to clone the gene for protein P. (a) How can a probe be prepared to identify the gene for protein P? (b) If we have prepared a radioactive messenger RNA as our probe in part (a), how could we verify that it is the mRNA for protein P? (c) If we wish to make a gene library from the DNA of human pancreatic cells, we proceed by digesting the DNA with the restriction enzyme BamHI and then separating the fragments by agarose gel electrophoresis. The fragments are transferred (by Southern blotting) onto a nitrocellulose filter and flooded with the radioactive probe. Following incubation, the filter is washed to remove any probe that has not specifically bound to one or more DNA fragments. Autoradiography of the filter reveals two bands of sizes 300 and 700 bp. When experiment is repeated using restriction enzyme Pstl, only one band of 1000 bp appears. If it is already known that pancreatic cells contain a single copy of the gene for protein P, which of these enzymes should be used to construct our gene library?