总RNA和mRNA来源的探针与cDNA芯片杂交的差异研究

提取BEP2D细胞的总RNA并按两种方式进行cDNA芯片探针的标记,一种是将100μg BEP2D细胞的总RNA利用逆转录法直接标记成荧光探针,另一种是先从100μg BEP2D细胞的总RNA中分离出mRNA,然后再标记成荧光探针。将两份标记好的探针同时与含有230个基因的cDNA芯片杂交。杂交后的芯片经Axon4100B扫描仪扫描,发现两种方式标记探针的一致性为93．04％,并且mRNA来源探针杂交后的荧光信号值较总RNA的弱。探讨了这两种方法标记探针在基因芯片表达谱研究中的差异性,目的是为利用这两种方法标记探针进行基因表达谱研究提供一些依据。     

Deoxyhypusine synthase from tobacco. cDNA isolation, characterization, and bacterial expression of an enzyme with extended substrate specificity.

Deoxyhypusine synthase catalyzes the formation of a deoxyhypusine residue in the translation eukaryotic initiation factor 5A (eIF5A) precursor protein by transferring an aminobutyl moiety from spermidine onto a conserved lysine residue within the eIF5A polypeptide chain. This reaction commences the activation of the initiation factor in fungi and vertebrates. A mechanistically identical reaction is known in the biosynthetic pathway leading to pyrrolizidine alkaloids in plants. Deoxyhypusine synthase from tobacco was cloned and expressed in active form in Escherichia coli. It catalyzes the formation of a deoxyhypusine residue in the tobacco eIF5A substrate as shown by gas chromatography coupled with a mass spectrometer. The enzyme also accepts free putrescine as the aminobutyl acceptor, instead of lysine bound in the eIF5A polypeptide chain, yielding homospermidine. Conversely, it accepts homospermidine instead of spermidine as the aminobutyl donor, whereby the reactions with putrescine and homospermidine proceed at the same rate as those involving the authentic substrates. The conversion of deoxyhypusine synthase-catalyzed eIF5A deoxyhypusinylation pinpoints a function for spermidine in plant metabolism. Furthermore, and quite unexpectedly, the substrate spectrum of deoxyhypusine synthase hints at a biochemical basis behind the sparse and skew occurrence of both homospermidine and its pyrrolizidine derivatives across distantly related plant taxa.