Masaki Izawa

Functional annotation of a full-length mouse cDNA collection

The RIKEN Mouse Gene Encyclopaedia Project, a systematic approach to determining the full coding potential of the mouse genome, involves collection and sequencing of full-length complementary DNAs and physical mapping of the corresponding genes to the mouse genome. We organized an international functional annotation meeting (FANTOM) to annotate the first 21,076 cDNAs to be analysed in this project. Here we describe the first RIKEN clone collection, which is one of the largest described for any organism. Analysis of these cDNAs extends known gene families and identifies new ones.The RIKEN Mouse Gene Encyclopaedia Project, a systematic approach to determining the full coding potential of the mouse genome, involves collection and sequencing of full-length complementary DNAs and physical mapping of the corresponding genes to the mouse genome. We organized an international functional annotation meeting (FANTOM) to annotate the first 21,076 cDNAs to be analysed in this project. Here we describe the first RIKEN clone collection, which is one of the largest described for any organism. Analysis of these cDNAs extends known gene families and identifies new ones.

Recognition Sites of 3′-OH Group by T7 RNA Polymerase and Its Application to Transcriptional Sequencing

When analyzing the elongation mechanisms in T7 RNA polymerase (T7 RNAP)by using site-directed mutagenesis and a protein expression system, we identified the recognition sites of the rNTP 3′-OH group in T7 RNAP. On the basis of three-dimensional crystal structure analysis, we selected and analyzed six candidate sites interacting with the 3′-OH group of rNTP in T7 RNAP. We found that the Phe-644 and Phe-667 sites are responsible for the high selectivity of T7 RNAP for rNTPs. Also, we constructed the protein mutations of these residues, F644Y and F667Y, which display a >200-fold higher affinity than the wild type for 3′-dNTPs. These findings indicate that the phenylalanine residues of 644 and 667 specifically interact with the 3′-OH group. Thus, these mutants, F644Y and F667Y, with incorporation of 3′-dNTP terminators, which is similar to native rNTPs, can offer low backgrounds and equal intensities of the sequencing ladders in our method, called “transcriptional sequencing.”

T7 RNA polymerase activation and improvement of the transcriptional sequencing by polyamines

We examined the possibility to improve the effectiveness of the in vitro transcription system using T7 RNA polymerase by coexistence with organic bases. The effect of the additives was evaluated by measuring the amount of RNA products in comparison with that of the control system (without additive). We found that four commercial bases and a series of ethylated polyamine analogues newly designed were active enhancers in the following activation order, 1,8-bis(ethylamino)octane > 1,8-octanediamine > 1,5-bis(ethylamino)pentane > cadaverine > 1,8-bis(ethylamino)-4-azaoctane > spermidine 1,18-bis(ethylamino)-5,14-diazaoctadecane > agmatine. It was shown that RNA products were corresponding, only in the presence of active enhancers, to the full length size of the template DNA, and that sequencing signals were enhanced by the presence of active enhancers with high fidelity so that the transcriptional sequencing was further refined to be a highly sensitive sequencing method from a small amount of linear dsDNA. These results suggest that T7 RNA polymerase was activated by the specific binding of the polyamine additive to produce RNA transcripts with fidelity to the template DNA. Therefore, it is expected that the transcriptional sequencing in the presence of active enhancers might be a powerful and sensitive method, in place of the prevalent DNA amplification method, for genomic science projects and clinical and practical gene diagnoses.

Practical application of transcriptional sequencing for GC-rich templates

Transcriptional sequencing (TS) is a method that differs considerably from conventional sequencing methods. These differences include the use RNA polymerases with rNTPs and 3′-dNTPs as substrates and terminators respectively, and initiation from double stranded promoters on templates of ds-DNA. We used TS in an attempt to sequence 33 clones whose electropherogram peaks suddenly became absent or weak with conventional sequencing methods. All of the TS reactions overcame the difficulty in sequencing the problematic target regions of the 33 clones. Therefore, TS can be applied to sequence not only GC-rich regions, but also whole genome sequences with a high GC content.