How can a large size eukaryotic gene insert be cloned?
Large size eukaryotic gene inserts cannot be cloned using regular plasmids because eukaryotic genes contain introns, which may be hundreds of kilobases in length. Even eukaryotic genes without introns exceed the maximum insert capacity of plasmids, which is only up to 10 kb.
Therefore, special vectors called 'artificial chromosomes' have been developed to carry huge lengths of eukaryotic DNA. These include Yeast Artificial Chromosomes (YACs), which can carry inserts of 200-500 kb, Bacterial Artificial Chromosomes (BACs) with capacity up to 300 kb, and Phage Artificial Chromosomes (PACs) carrying 100-300 kb. These high capacity cloning vectors enable successful cloning of large eukaryotic genes.
Explanation
The textbook context explains that eukaryotic genes are much larger than prokaryotic genes due to introns. Regular plasmid vectors (capacity 10 kb) and even bacteriophage vectors (8-25 kb) cannot accommodate such large inserts. The context introduces artificial chromosomes (YAC, BAC, PAC) as the solution, with YACs having the highest capacity (200-500 kb). Table 2.2 provides the specific insert size capacities for each vector type.