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(2001) The complete gene sequence ot titin, expression of an unusual approximately 700-kDa titin isoform, and its interaction with obscurin identify a novel Z-line to I-band linking system. Circ. Res. 89, 1065–1972 25 Fukuzawa, A. et al. (2001) Invertebrate connectin spans as much as 3.5 μm in the giant sarcomeres of crayfish claw muscle. EMBO J. 20, 4826–4835 26 Machado, C. and Andrew, D.J. (2000) D-Titin: a giant protein with dual roles in chromosomes and muscles. J. Cell Biol. 151, 639–652 Koscak Maruyama National Center for University Entrance Examinations, Meguro, Tokyo 153-8501, Japan. e-mail: k_inoke@cen.dnc.ac.jp Forum Computer Corner Today, several resources for obtaining sequence information on human transcripts are available. These can provide merely sequence information or, in addition, a cDNA clone [e.g. an expressed sequence tag (EST) clone] that encodes part of the open reading frame (ORF). UniGene is an example of a database in which over three million human EST sequences have been assembled to provide ~96 000 gene clusters. However, obtaining the physical full-length cDNA clone, or at least one that contains the entire ORF, from a gene of interest is not easy. Several public and private groups have focused on generating full-length cDNA libraries with a view to providing these clones, either free or for a charge. The advantages of full-length cDNA or full-length cDNA-enriched libraries cannot be overestimated. Having to screen many rounds of partial clones, or performing 5′ or 3′ RACE (rapid amplification of cDNA ends), to obtain a full-length cDNA might not only be tedious but is often unsuccessful. Therefore, the possibility of being able to go directly to a computer and order a full-length clone is an attractive option. Even in cases where an investigator requires a well-known and characterized gene, the task of obtaining the cDNA from another group is not always easy. Recent developments in techniques for obtaining full-length cDNAs have greatly improved the quality of cDNA libraries. Most of these techniques are based on selectively amplifying mRNA containing the 5′ cap structure which, in principle, ensures that the 5′ end is not truncated. Some of the methods in use today are oligo-capping [1], CAPtrapper [2], CAPture [3] and SMART™ (Clontech). Additionally, simply selecting larger mRNAs based on their size can be used to enrich for potentially full-length cDNAs [4]. Box 1 shows some of the features of any cDNA source that must be evaluated before ordering a clone. For instance, the clones might not be fully sequenced or could be in prokaryotic, but not mammalian, expression vectors. Box 2 shows a list of the major sources of full-length mouse or human cDNAs available today. It is expected that we will have a full set of sequence-verified human and mouse ORFs within the next 2–3 years as is already the case with yeast ORFs. Resources for full-length cDNAs Troels Z. Kristiansen and Akhilesh Pandey Size and quality of the cDNA collection How many clones does the cDNA resource provide? Is the cDNA clone sequence verified (errors can be introduced during reverse transcription and polymerase chain reaction steps)? How is the cDNA provided? Mammalian expression vector or prokaryotic cloning vector? Tagged with an epitope? Can the cDNA insert be shuttled to other functional vectors; for example, by recombination-based cloning? Bioinformatics capabilities Is there a BLAST search interface, or provision for searching by gene name, accession number or protein domain? Alternative splicing If several splice variants of a gene are known to occur, which one is provided? Box 1. Evaluating a ‘full-length’ cDNA resource