Function of Pro-185 in the ProCys of conserved motif IV in the EcoRII [cytosine-C5]-DNA methyltransferase

ProCys in the conserved sequence motif IV of [cytosine-C5]-DNA methyltransferases is known to be part of the catalytic site. The Cys residue is directly involved in forming a covalent bond with the C6 of the target cytosine. We have found that substitution of Pro-185 with either Ala or Ser resulted in a reduced rate of methyl group transfer by the EcoRII DNA methyltransferase. In addition, we observed an increase in the Km for substrate S-adenosyl-L-methionine (AdoMet), but a decrease in the Km for substrate DNA. This is reflected in minor changes in kcat/Km for DNA, but in 10- to 100-fold reductions in kcat/Km for AdoMet. This suggests that Pro-185 is important to properly orient the activated cytosine and AdoMet for methyl group transfer by direct interaction with AdoMet and indirectly via the Cys interaction with cytosine.     

Effects of age on phenomenology and consistency of flashbulb memories of September 11 and a staged control event.

In two studies, the special status of flashbulb memories was investigated by contrasting the effects of age on the phenomenology and consistency of flashbulb memories of September 11, over a 2-year delay period, with those of a mundane staged control event: participants learning that they had not won a small prize. Flashbulb memories produced no significant age effects for either phenomenological characteristics or test–retest consistency, as predicted by Mather's (2004) emotional compensation hypothesis. By contrast, the control event resulted in significant age effects for phenomenological characteristics (e.g., specificity and the amount of detail recalled) but not for test–retest consistency. Furthermore, in both age groups, memories of September 11 were significantly more vivid, detailed, and consistent than control memories even though the test–retest interval was twice as long for flashbulb memories. In addition, correlations between consistency scores and ratings of rehearsal were positive for control memories but negative for flashbulb memories. The theoretical implications of these findings for research on cognitive aging and flashbulb memories are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Differential effects of age on involuntary and voluntary autobiographical memory.

Research on aging and autobiographical memory has focused almost exclusively on voluntary autobiographical memory. However, in everyday life, autobiographical memories often come to mind spontaneously without deliberate attempt to retrieve anything. In the present study, diary and word-cue methods were used to compare the involuntary and voluntary memories of 44 young and 38 older adults. The results showed that older adults reported fewer involuntary and voluntary memories than did younger adults. Additionally, the life span distribution of involuntary and voluntary memories did not differ in young adults (a clear recency effect) or in older adults (a recency effect and a reminiscence bump). Despite these similarities between involuntary and voluntary memories, there were also important differences in terms of the effects of age on some memory characteristics. Thus, older adults’ voluntary memories were less specific and were recalled more slowly than those of young adults, but there were no reliable age differences in the specificity of involuntary memories. Moreover, older adults rated their involuntary memories as more positive than did young adults, but this positivity effect was not found for voluntary memories. Theoretical implications of these findings for research on autobiographical memory and cognitive aging are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)