843 research outputs found
Genome-wide organization of eukaryotic pre-initiation complex is influenced by nonconsensus protein-DNA binding
Genome-wide binding preferences of the key components of eukaryotic
pre-initiation complex (PIC) have been recently measured with high resolution
in Saccharomyces cerevisiae by Rhee and Pugh (Nature (2012) 483:295-301). Yet
the rules determining the PIC binding specificity remain poorly understood. In
this study we show that nonconsensus protein-DNA binding significantly
influences PIC binding preferences. We estimate that such nonconsensus binding
contribute statistically at least 2-3 kcal/mol (on average) of additional
attractive free energy per protein, per core promoter region. The predicted
attractive effect is particularly strong at repeated poly(dA:dT) and
poly(dC:dG) tracts. Overall, the computed free energy landscape of nonconsensus
protein-DNA binding shows strong correlation with the measured genome-wide PIC
occupancy. Remarkably, statistical PIC binding preferences to both
TFIID-dominated and SAGA-dominated genes correlate with the nonconsensus free
energy landscape, yet these two groups of genes are distinguishable based on
the average free energy profiles. We suggest that the predicted nonconsensus
binding mechanism provides a genome-wide background for specific promoter
elements, such as transcription factor binding sites, TATA-like elements, and
specific binding of the PIC components to nucleosomes. We also show that
nonconsensus binding influences transcriptional frequency genome-wide
The Computational Power of Beeps
In this paper, we study the quantity of computational resources (state
machine states and/or probabilistic transition precision) needed to solve
specific problems in a single hop network where nodes communicate using only
beeps. We begin by focusing on randomized leader election. We prove a lower
bound on the states required to solve this problem with a given error bound,
probability precision, and (when relevant) network size lower bound. We then
show the bound tight with a matching upper bound. Noting that our optimal upper
bound is slow, we describe two faster algorithms that trade some state
optimality to gain efficiency. We then turn our attention to more general
classes of problems by proving that once you have enough states to solve leader
election with a given error bound, you have (within constant factors) enough
states to simulate correctly, with this same error bound, a logspace TM with a
constant number of unary input tapes: allowing you to solve a large and
expressive set of problems. These results identify a key simplicity threshold
beyond which useful distributed computation is possible in the beeping model.Comment: Extended abstract to appear in the Proceedings of the International
Symposium on Distributed Computing (DISC 2015
Classical Bound for Mach-Zehnder Super-Resolution
The employment of path entangled multiphoton states enables measurement of
phase with enhanced precision. It is common practice to demonstrate the unique
properties of such quantum states by measuring super-resolving oscillations in
the coincidence rate of a Mach-Zehnder interferometer. Similar oscillations,
however, have also been demonstrated in various configurations using classical
light only; making it unclear what, if any, are the classical limits of this
phenomenon. Here we derive a classical bound for the visibility of
super-resolving oscillations in a Mach-Zehnder. This provides an easy to apply,
fundamental test of non-classicality. We apply this test to experimental
multiphoton coincidence measurements obtained using photon number resolving
detectors. Mach-Zehnder super-resolution is found to be a highly distinctive
quantum effect.Comment: 4 pages, 4 figure, Comments welcom
NXNSAttack: Recursive DNS Inefficiencies and Vulnerabilities
This paper exposes a new vulnerability and introduces a corresponding attack,
the NoneXistent Name Server Attack (NXNSAttack), that disrupts and may paralyze
the DNS system, making it difficult or impossible for Internet users to access
websites, web e-mail, online video chats, or any other online resource. The
NXNSAttack generates a storm of packets between DNS resolvers and DNS
authoritative name servers. The storm is produced by the response of resolvers
to unrestricted referral response messages of authoritative name servers. The
attack is significantly more destructive than NXDomain attacks (e.g., the Mirai
attack): i) It reaches an amplification factor of more than 1620x on the number
of packets exchanged by the recursive resolver. ii) In addition to the negative
cache, the attack also saturates the 'NS' section of the resolver caches. To
mitigate the attack impact, we propose an enhancement to the recursive resolver
algorithm, MaxFetch(k), that prevents unnecessary proactive fetches. We
implemented the MaxFetch(1) mitigation enhancement on a BIND resolver and
tested it on real-world DNS query datasets. Our results show that MaxFetch(1)
degrades neither the recursive resolver throughput nor its latency. Following
the discovery of the attack, a responsible disclosure procedure was carried
out, and several DNS vendors and public providers have issued a CVE and patched
their systems
Fast Consensus under Eventually Stabilizing Message Adversaries
This paper is devoted to deterministic consensus in synchronous dynamic
networks with unidirectional links, which are under the control of an
omniscient message adversary. Motivated by unpredictable node/system
initialization times and long-lasting periods of massive transient faults, we
consider message adversaries that guarantee periods of less erratic message
loss only eventually: We present a tight bound of for the termination
time of consensus under a message adversary that eventually guarantees a single
vertex-stable root component with dynamic network diameter , as well as a
simple algorithm that matches this bound. It effectively halves the termination
time achieved by an existing consensus algorithm, which also works under
our message adversary. We also introduce a generalized, considerably stronger
variant of our message adversary, and show that our new algorithm, unlike the
existing one, still works correctly under it.Comment: 13 pages, 5 figures, updated reference
- …